Preface
Summary
The question addressed in this book is whether metaphysics is
possible. If metaphysics is a science, why are we unable to make
progress or reach unanimous agreements as we can with the other
sciences? And if it is not a science, on what grounds do its claims
to truth rest? At the moment, there is no standard for agreement on
metaphysical questions, so there is no objective means for settling
disagreements. As a result, all sorts of opinions are tossed about
with no means of reaching definite conclusions.
The question of whether metaphysics is possible implies that the
validity of metaphysics can be doubted. This implication may upset
many readers: we don't like being told that a subject we have
studied intensively might be useless. Nevertheless, Kant has become
aware that metaphysics needs a sturdier foundation than it currenty
has if it is to be taken seriously. He is confident that those who
read his work carefully will agree.
Kant came to recognize the importance of finding a sturdy
foundation for metaphysics when he read Hume, whom he claims roused
him from a "dogmatic slumber." Hume inspired Kant by critiquing our
concept of cause and effect, asking how we know that one event acts
as a cause for another event. Hume concludes that we do not have a
priori knowledge of causation: we cannot know the causal
relationship between two events prior to our experience of it by
means of reason alone. Instead, Hume suggests that what we call our
"knowledge" of cause and effect is simply an expectation that one
event will follow another based on habit rather than reason.
Hume's conclusion is fatal to metaphysics. If our "knowledge" of
cause and effect is based on custom and habit rather than reason,
then all the metaphysical theories that try to explain how our
reason leads us to this knowledge are in vain. On further
inspection, Kant found that all metaphysics is based on a priori
reasoning, drawing connections between concepts without any
reference to experience, so all metaphysics is potentially open to
Hume's attack.
Kant explains how connections can be drawn a priori and how
metaphysics is possible in his monumental Critique of Pure Reason.
This book is long and difficult, however, and so he has written the
Prolegomena to any Future Metaphysics as a shorter work that will
make the ideas found in the Critique more accessible to a wider
audience. The Critique of Pure Reason follows what Kant calls a
"synthetical" style, deducing conclusions from first principles.
The Prolegomena, on the other hand, follows an "analytical" style,
breaking the problem down into simple bits and examining them
individually.
Commentary
Metaphysics is the oldest and most respected branch of
philosophy. It examines the constitution, nature, and structure of
reality, and strives to uncover the underlying causes and
foundations that make things the way they are. Physics simply
describes the universe, and the laws of physics are only good for
predicting what will happen. Metaphysics, by contrast, tries to
explain the universe and why things happen the way they do. While
physics is based on observation and experience, metaphysics is an a
priori form of knowledge based on the unaided exercise of pure
reason. Metaphysicians do no experiments: they try to sort
everything out in their heads.
The nature of causation is an important topic in metaphysics. We
can see in our day to day life that certain events seem to cause
other events: one billiard ball may cause another billiard ball to
move, or a fall from a great height may be the cause of a broken
leg. The metaphysical question, then, is why and how one event can
act as a cause for another. How do we know that a certain event is
the cause of a later event, and not just a coincidental precedent?
What is the nature of the causal connection between the two?
Hume's answer, in short, is that there is no discernable
difference between two events that are related causally and two
events that are just coincidentally conjoined. He argues that we
say two events are causally connected if we see them frequently
conjoined. Hume does not believe that we have a rational
justification for doing so. We do not and cannot perceive the
causal connection itself, and all our talk about cause and effect
is based simply on the habit of seeing certain events happen one
after another.
Kant notes that Hume's argument is an attack on the very
possibility of doing metaphysics. Metaphysics tries to look behind
the events themselves and see the fundamental connections and inner
workings that tie things together. As a result, metaphysics relies
on the assumption that the intellect has the power to see these
fundamental connections and inner workings even if the senses do
not. Hume's assertion that the intellect has no such power is thus
a fatal blow to the very study of metaphysics.
Kant is willing to agree with Hume, but he is not as content as
Hume is to simply conclude that metaphysics is misguided. Kant
concludes instead that metaphysics is in need of clearer definition
and stronger foundation if it is to be taken seriously. He
complains that metaphysics is unscientific, that there are no
standards for right and wrong, and that anybody's opinion is as
good as anybody else's.
Kant's project, then, is to make metaphysics scientific. This
means turning metaphysics into a systematic body of knowledge built
on first principles. Newtonian physics, for instance, begins with
Newton's three laws, which are based on careful observation and
experience. Further physical principles are then deduced from these
three laws. A new proposition can then be judged to be true or
false quite easily based on whether or not it accords with the laws
and principles that are already in place. Kant hopes to do the same
for metaphysics so that disagreements and criticisms regarding
metaphysical problems can be settled objectively, once and for
all.
This project is part of what is called Kant's "critical" period.
In his early career, he followed in the footsteps of rationalist
metaphysicians such as Descartes, Leibniz, and Christian Wolff. The
influence of Hume led Kant to write his three great "critiques":
the Critique of Pure Reason, the Critique of Practical Reason, and
the Critique of Judgment. These works, along with the Prolegomena,
are "critiques" because they do not simply try to answer
metaphysical questions, but ask instead how we know or how we claim
to know the answers to these questions. Kant is primarily
interested in knowing, for instance, how we can know that two
events are connected causally, rather than what the nature of that
causal connection is.
Preamble
Summary
Metaphysics consists of knowledge apprehended by pure reason. By
definition, metaphysics studies what is beyond experience. The
Greek root meta means "beyond," so "metaphysics" literally means
"beyond physics." Like mathematics, metaphysics is an a priori body
of knowledge.
The distinction between a priori and a posteriori ways of
thinking is that the former are drawn from pure reason and the
latter are drawn from experience. Kant goes on to draw a second,
even more important, distinction between analytic and synthetic
judgments.
The predicate of an analytic judgment is contained in the
concept of the subject: the predicate, then, is simply an analysis
of the subject concept. "All bachelors are unmarried" is analytic:
being unmarried is a part of the concept of "bachelor," so saying
that all bachelors are unmarried doesn't add anything to our
concept of "bachelor"; it just clarifies the definition.
The predicate of a synthetic judgment, on the other hand, adds
something new to the concept of the subject: it synthesizes two
different cognitions. "All swans are white" is synthetic: we can
know what a swan is without necessarily knowing that it's white, so
learning that swans are white is an additional cognition that we
can attach to our concept of "swan."
All analytic judgments are a priori, since they consist simply
in the analysis of concepts and do not appeal to experience.
Synthetic judgments, on the other hand, can be either a priori or a
posteriori. Kant classifies synthetic judgments into three types:
judgments from experience, mathematical judgments, and metaphysical
judgments.
Judgments from experience are synthetic a posteriori since they
are pieced together (synthetic) from the objects of experience (a
posteriori).
Mathematics consists of synthetic a priori judgments. The
concept of "7 + 5," Kant argues, contains the union of those two
numbers in a single number, but the concept itself does not contain
the number 12. We must make a leap of intuition in order to
determine that twelve is indeed the number that results from the
union of seven and 5. The same is true of geometry: the concept of
the shortest distance between two points is not contained within
the concept of a straight line. The temptation to think of math as
analytic comes from the fact that the truths of mathematics are
necessary: we cannot reasonably deny that 7 + 5 = 12. The fact of
the matter is that mathematical cognitions require intuitive leaps
that are synthetic in nature.
Metaphysics also consists of synthetic a priori judgments. It
may seem that metaphysics consists largely of analytic judgments,
since the only thing metaphysicians agree upon are the various
definitions that are analytic in nature. However, metaphysics
consists of synthetic judgments that are built upon these analytic
definitions, much like mathematics consists of synthetic judgments
built upon analytic axiomatic truths.
The need to ask whether metaphysics is even possible arises
because there is little agreement over the synthetic judgments that
ought to constitute it as a body of knowledge. Kant's proposed
method is to start with the assumption that synthetic a priori
judgments are possible, since they constitute both mathematics and
pure natural science. He will investigate how synthetic a priori
knowledge is possible in these fields in the hopes of discovering
also how such knowledge might become a reliable source for
metaphysics. He proposes to examine first mathematics, then pure
natural science, and then ask how metaphysics is possible in
general and as a science.
Commentary
The distinction between a priori and a posteriori shows the two
possible sources of knowledge: the intellect and experience. If we
can know something independently of experience, it is a priori, and
if we know something through experience, it is a posteriori. Math
is a paradigmatic example of a priori knowledge: I can figure out
that 7 + 5 = 12 in my head, and nothing I find in experience can
possibly contradict that knowledge. The statement "all bachelors
are unmarried" is also a priori even though it refers to bachelors,
which, unlike numbers, can be found in the world outside our heads.
The reason is that "all bachelors are unmarried" is a definition of
a bachelor rather than a statement based on experience. The
statement, "all bachelors are lonely," on the other hand, is a
posteriori, since loneliness is not a part of the concept of
"bachelor." That statement is drawn from the speaker's experience
with bachelors or from what other people have told him about
bachelors.
While the a priori/a posteriori distinction is epistemological,
distinguishing between sources of knowledge, the analytic/synthetic
distinction deals with the logical structure of the judgments
themselves. "All bachelors are unmarried" is analytic because the
concept of bachelor is "unmarried man": this statement merely
clarifies a part of the concept of "bachelor." A good test for
whether a statement is analytic is to ask whether people could
understand the subject concept if they did not know that the
predicate were true of it. For instance, if I did not know that all
bachelors are unmarried, I couldn't properly be said to understand
what a bachelor is. On the other hand, "all swans are white" is
synthetic because, even though we may generally think of white
animals when we think of swans, I could be said to understand what
a swan is without knowing that it is white.
Kant was the first person to draw the analytic/synthetic
distinction explicitly. Until Kant, this distinction had generally
been lumped together with the a priori/a posteriori distinction.
Hume and others had considered the propositions of mathematics to
be analytic. In proposing that there are synthetic a priori
judgments, Kant suggests, contrary to conventional wisdom, that
propositions like "7 + 5 = 12" are in fact synthetic. His argument
is essentially that the concept of "7 + 5" is the union of the
concepts of "7," "5," and addition. None of those three concepts in
themselves contain the concept of "12"; it is a new concept that
arises from the synthesis of the three subject concepts.
There are further arguments in Kant's favor. If concept of "12"
were part of the concept of "7 + 5," then so would the concepts of
"9 + 3" and "16 - 4," and an infinitude of other concepts. How
could the concept of "7 + 5" possibly contain all these other
concepts? Also, it seems ridiculous to suggest that the concept of
"154,938" is a part of the concept of "52,624 + 102,314": we could
understand the concept of that sum without necessarily knowing what
the two numbers add to.
While analytic judgments consist simply of analyzing the subject
of a proposition, synthetic judgments add something new to it. They
effectively connect two independent pieces of knowledge to each
other. Kant explores the nature of this connection. With synthetic
a posteriori knowledge, the connection is made through experience.
If I see a lot of white swans, I come to associate the concept of
white with the concept of swan through experience. With synthetic a
priori knowledge, the answer is more complicated. How do I learn to
link the concept of "7 + 5" with the concept of "12"? In the
sections that follow, Kant sets about trying to answer that
question. His hope is that if he can explain how we can connect
concepts in pure mathematics and pure natural science, he will also
be able to explain how we can connect concepts in metaphysics.
The analytic/synthetic distinction is one of Kant's most
significant contributions to philosophy. Like any significant
contribution, it has been the subject of heated controversy ever
since. One of the difficulties lies in saying precisely what the
concept of "bachelor" or "swan" consists of. At what point can I no
longer properly be said to understand what a thing is? If all
humans are animals and all humans have noses, why is being an
animal a part of the concept of being human and having a nose not?
The idea that words have "concepts" attached to them goes all the
way back to Aristotle's essences.
First Part
Summary
The first of the four questions Kant sets himself in the
preamble is "how is pure mathematics possible?" If math consists of
synthetic a priori cognitions, we must be able to draw connections
between different concepts by means of some form of pure intuition.
The word translated as "intuition" is the German word Anschauung,
meaning literally a point of view or way of seeing. For Kant,
intuition connects the two distinct concepts that are joined in
synthetic judgments. Kant distinguishes between empirical
intuitions and pure intuitions. Empirical intuition is what we
normally call sense perception: in the synthetic proposition, "my
cat has brown fur," my sense experience, or empirical intuition,
leads me to connect the concept of "my cat" with the concept of
"has brown fur" (this is not Kant's example).
Since math consists of synthetic a priori cognitions, there must
be some form of pure intuition innate within us that allows us to
connect different concepts without reference to sense experience.
Kant's answer is that space and time are not things in themselves,
to be found in the world, but are what he calls the "form of
sensibility": they are innate intuitions that shape the way we
perceive the world. Prior to any sense experience, we have no
concept of the objects we find in space and time, but we still have
the concepts of space and time themselves. Geometry is the a priori
study of our pure intuition of space, and numbers come from the
successive moments of our pure intuition of time. If space and time
were things in themselves that we could only understand by
reference to experience, geometry and math would not have the a
priori certainty that makes them so reliable.
Neither space nor time, nor the objects we perceive in space and
time, are things in themselves: the objects we perceive are mere
appearances of things in themselves, and space and time are empty
forms that determine how things appear to us. If space were actual
and not built into of our mental framework, two things with all the
same properties would be in every way identical. However, Kant
points out, our left and right hands have all the same properties,
but they are not identical: a left hand glove will not fit on a
right hand. This suggests that space is not independent of the mind
that perceives it.
These conclusions lead Kant to three final remarks. First, he
points out that we can have a priori certainty of geometry, and
thus of our understanding of spatial relations, only because we
have a pure intuition of space. Our certainty comes because we are
only examining our own mental framework, and not things in the
world. Second, he responds to the potential accusation that he is
engaging in idealism. Idealism claims that there are no objects in
the world, only minds, and that everything we see is just a
construction of the mind. Though Kant has argued that we cannot
perceive things in themselves, but only appearances of things, he
still maintains that things in themselves, independent of our
perception, exist, and that they are the source of what we do
perceive. Third, he points out that appearances cannot be
deceptive. I can misinterpret what I see, and be deceived in this
way, but I cannot be mistaken about the appearances themselves. If
space and time were things in themselves, then we could
misinterpret our perception of them and be deceived regarding them.
However, since they are mere appearances, they are a priori
certain.
Commentary
In the preface to the second edition of the Critique of Pure
Reason, Kant claims his system has caused a "Copernican revolution
in philosophy." The revolution he refers to is a reversal of our
concept of space and time. Until Kant, it had been assumed that
space and time were properties of the world, into which the objects
of sensory experience were placed. Kant's radical reversal consists
in claiming that space and time are not properties of the world but
are rather properties of the perceiving mind. Space and time are
like mental spreadsheets that organize how information is organized
in our minds. Bertrand Russell explains this idea: "If you always
wore blue spectacles, you would be sure of seeing everything blue.
Similarly, since you always wear spatial spectacles in your mind,
you are sure of always seeing everything in space."
Kant's argument for this position starts from the assumption
that geometry and mathematics consist of synthetic a priori
cognitions. To make synthetic judgments a priori, we must have some
sort of pure intuition that allows us to draw concepts together
without making any reference to experience. Geometry, for instance,
gives us a priori knowledge about space, so our knowledge of space
must be built into our minds. Therefore, Kant concludes, our
concept of space is not something we learn from experience, but it
is something we have prior to experience. Our concept of space is a
feature of our minds and not a feature of reality. Kant believes he
can make a similar argument about our concept of time with
reference to our synthetic a priori knowledge of arithmetic.
If computers had existed in Kant's time, he would have had a
useful metaphor for explaining the relationship between things in
themselves, appearances, and our perceiving mind. We can compare
things in themselves to data. Data in itself is invisible, and yet
the programs we run are nothing more than data being interpreted.
We can "read" data only once it's been through a processor and then
projected onto a monitor. What we see on the monitor is not the
data itself, but the "appearance" of the data. The processor and
the monitor are like the pure intuitions of space and time: we
cannot understand the thing in itself (data) until it has been made
comprehensible by these intuitions. We do not perceive things in
themselves but appearances of things. Our minds do not have the
capacity to understand things in themselves just as we cannot
understand data in itself by staring at a microchip.
Kant's discussion of space as an a priori form of intuition is
meant to settle a debate between Newton and Leibniz regarding the
nature of space. Newton maintains that space is absolute: it exists
already as a thing in itself independently of the things that are
in it. Leibniz holds to a relational theory of space, according to
which space is a relational property that holds between objects.
Space is not absolute, but dependent on the objects that are in
it.
Both positions share the assumption that space is
mind-independent. Though Leibniz does not, like Newton, believe
that space is absolute, he believes that space only depends on the
relations between objects and not on the minds that perceive space.
Kant's example of how two internally identical hands cannot fit the
same glove is meant to contradict Leibniz.
At the beginning of the twentieth century, with Einstein's
theory of relativity, Kant's theory of space became the subject of
heated controversy. According to Kant, our knowledge of space comes
prior to experience, and Euclidean geometry can tell us everything
we need to know about space. General relativity shows that the
universe does not in fact conform to the laws of Euclidean geometry
and that space and time are far more complicated than we think.
Space and time, far from being pure intuitions that we can know a
priori, are quite different from what our intuition tells us they
are.
Kantians reply to this objection by saying that Kant is not
talking about time and space in themselves but just about our
cognition of time and space. Though space-time may be a
four-dimensional curved space, our mind perceives space as flat,
three-dimensional, and independent of time. Kant is not making a
statement about how the world is, but about how the mind perceives
the world.
The arguments for both sides are complicated, but over the
course of the century, the defenders of Kant have diminished in
number. The new physics of relativity and quantum mechanics have
increasingly showed that any "intuitions" we might have about the
nature or structure of reality are liable to be mistaken. Though
Kantian constructions are arguably possible, this new physics makes
a lot more sense if we assume that space-time exists independently
of the mind.
Second Part, Sections 1426
Summary
The second part of the Prolegomena concerns itself with the
question, "how is pure natural science possible?" "Natural science"
is what nowadays we would simply call "science": it is the
systematic body of knowledge that deals with nature. Kant remarks
first of all that when we talk about nature we are not talking
about things in themselves, which, as he has already claimed, we
can know nothing about. Rather, we are talking about the objects of
experience as they appear to us. For our study of nature to be a
science, these experiences must conform to universal and necessary
laws. Kant observes that we do indeed study natural science and
make use of universal and necessary laws. There is some kind of
pattern or regularity in our experience, but how is this
possible?
Kant draws a distinction between judgments of perception and
judgments of experience. Judgments of perception bring together
several empirical intuitions and are only subjectively valid. For
instance, I may see the sun shining brightly and feel that a rock
under the sun's rays is warm, and judge that the rock grows warm
under the sun. This judgment draws together the intuitions that the
sun is shining and the rock is warm, but it is still valid only for
me and only at that particular time.
Judgments of experience apply pure concepts of the understanding
to judgments of perception, turning them into objective,
universally valid laws. For instance, I can apply the concept of
cause to my earlier judgment that the rock grows warm under the sun
and judge that the sun caused the rock to grow warm. We do not find
pure concepts of the understanding in experience. Rather, they are
concepts we use to structure our understanding of experience. They
are a priori concepts we use to draw together and make sense of our
various judgments of perception. Because these concepts are a
priori, they are also universal and necessary. Thus, judgments of
experience are the synthetic a priori laws that make natural
science possible.
Essentially, the distinction is that judgments of perception
deal only with what we sense, or intuit, while judgments of
experience deal with what we infer from our perceptions. We cannot
dispute judgments of perception because they are wholly subjective:
you cannot tell me the car didn't seem red to me. We can dispute
judgments of experience because they are meant to be objective: you
can tell me the car wasn't red.
Section twenty-one categorizes the different kinds of judgments,
concepts of the understanding, and universal principles of natural
science into three separate tables. These tables are reproduced in
a special section in this SparkNote entitled "Kant's Tables of
Categories."
The table of judgments divides judgments into their logical
parts. Every judgment must have one of the three kinds of quantity,
quality, relation, and modality. For instance, the judgment "the
sky is blue" is singular (it deals with the sky), affirmative (it
affirms that the sky is blue), categorical (it is a simple
subject-predicate sentence), and assertoric (it makes an
assertion).
The table of the concepts of the understanding lists the
concepts that correspond to the logical parts of judgments. By
applying a concept to the corresponding judgment, we can turn a
judgment of perception into a judgment of experience. For instance,
the concept that corresponds to an assertoric judgment is
"existence," so we can make the objective judgment that a blue sky
exists.
The table of universal principles classifies four different
kinds of law that correspond to the four different kinds of
concepts of the understanding.
Commentary
Kant is complicated, but there is a very clear structure hiding
underneath all this difficult vocabulary. Essentially, Kant is
building a complex system to explain how we make sense of the
world.
At a very basic level, Kant distinguishes between things in
themselves, and our perceiving mind. The first question is how can
we perceive things in themselves? How does our mind make contact
with anything outside it? Kant answers that we cannot perceive
things in themselves directly; all we can perceive are sensations,
the impression things in themselves make upon our senses.
Our mind perceives sensations, but must impose some sort of form
on these sensations for them to be intelligible. This form is our
intuition of space and time. By subjecting the sensations we
perceive to the intuitions of space and time, we get empirical
intuitions. Empirical intuitions are what we might refer to as
"sense-data": they are what I see, hear, or feel at any given
moment.
If all I had were empirical intuitions, life would be a
meaningless blur of unintelligible sensations. In order to make
sense of experience, we must first draw connections between
empirical intuitions. Judgments of perception join two or more
intuitions, associating them with one another. Seeing the bright,
shining sun and feeling the warm rock are two separate empirical
intuitions: a judgment of perception makes a connection between the
two.
Judgments of perception are subjective. I can draw a connection
between the sun and the warm rock, but I can't relate that
connection to any of my past or future experience, and I can't
relate it to anyone else's experience. Empirical intuitions and
judgments of perception come from our faculty of sensibility, which
deals with our senses and what they tell us. To give objectivity or
universality to our experience, we must subject it to our faculty
of understanding, which deals with our capacity for thought and
concept formation.
Kant infers that we must use concepts of pure understanding to
turn judgments of perception into judgments of experience because
empirical intuitions in themselves cannot be generalized. Judgments
of perception are particular and subjective: only a priori concepts
can be universal and objective. As Hume was right to observe, we
cannot find universal concepts like "every event is caused" in
experience. Kant concludes that such concepts are a part of the
understanding: we do not find them in experience; we apply them to
experience.
Kant has a two-step schema that explains how we come to see the
world. In the first step, which deals with our faculty of
sensibility, we have things in themselves providing sensations that
are then given subjective form by our pure intuitions of space and
time. Sensations combined with pure intuitions make empirical
intuitions. In the second step, which deals with our faculty of
understanding, these empirical intuitions are given objective form
by the pure concepts of the understanding. Empirical intuitions
combined with pure concepts of the understanding make the
appearances that constitute experience.
We should not mistake Kant's system for elaborate psychology. He
is not giving a map of the human mind, or explaining how it is that
we come to cognize things. Rather, he is examining what we find in
experience, and analyzing its parts. His procedure is logical
rather than psychological. He recognizes, for instance, that we
have a concept of cause and effect, but that that concept cannot
possibly be derived from experience. Thus, he concludes that we
must have some faculty that leads us to see the world in terms of
cause and effect. Similarly, he argues that our understanding of
time and space cannot itself be found in experience, and so must
also rely on our intuition.
Ultimately, mere sensations constitute very little of what we
consider to be our experience of the world. A great deal of our
experience comes from our inner faculties. Though none of these
faculties can actually "say" anything themselves, they give shape
and form to our sensations, and thus deeply influence how we
experience them.
Second Part, Sections 2739
Summary
Hume's skepticism arises when he asks how we perceive causal
connections between events. Reason alone cannot tell us about
connections between things in the world, and experience alone
cannot infer universal generalizations such as "every event has a
cause." Hume concludes that in fact we have no rationally justified
knowledge of cause and effect. He suggests instead that our concept
of causation is justified only by the habit of seeing certain
events follow from certain other events.
Kant agrees that we cannot discover the concept of cause and
effect either in experience or by means of reason. However, he does
not conclude with Hume that this concept is merely a result of
habit or custom.
Rather, he suggests, causation is an a priori concept of the
understanding applied to appearances. We can know nothing about
things in themselves; we can know only how they appear to us in the
form given to them by our faculties of sensibility and
understanding. The concept of cause and effect is not to be found
in these appearances; rather, it is part of the form given to them
by the understanding. Causation is not a "thing" that we can
discover, either by means of reason or experience. Causation is a
form given to experience that makes it intelligible to us. Hume
asked how we can derive pure concepts (such as causation) from
experience, and answered that we cannot. Kant agrees: we cannot
derive pure concepts from experience; rather, we derive experience
from these pure concepts.
Pure concepts of the understanding make experience legible, so
to speak, but cannot tell us anything about things in themselves.
Because pure concepts, as well as our pure intuitions of space and
time, are a priori and therefore necessary, we are tempted to think
that they can give us knowledge beyond that which we find in
experience. However, our pure concepts and pure intuitions provide
only form, and no content. They help us make connections between
appearances, and as such, they deal only on the level of
appearances. They cannot tell us anything about the things in
themselves behind these appearances.
Nature, understood as the totality of all our sensations, is
possibleas we saw in the first partby means of our pure intuitions
of space and time. Nature, understood as the totality of experience
as understood and connected by laws, is possibleas we saw in this
part by means of our pure concepts of the understanding. We cannot
go farther and ask how the faculties that give us our pure
intuitions and pure concepts are possible, because it is precisely
these faculties that help us make sense of experience. We have no
further faculty that would help us understand what is behind these
faculties.
Sensations themselves teach us nothing about the connections
between them or the laws that govern them: these are all provided
by our faculties of sensibility and understanding. These faculties,
then, are what make nature itself possible, insofar as nature is
our intelligible experience. Whatever laws or universality we find
in experience comes not from the sensations themselves but from the
form given to them by our faculties. Thus, Kant concludes: "the
understanding does not derive its laws (a priori) from, but
prescribes them to, nature."
Kant wraps up this part with an example showing how we derive
astronomical principles from our pure intuition and concepts rather
than from experience itself, and with an appendix discussing his
system of categories.
Commentary
Early modern philosophy, from Descartes to Hume, is roughly
divided between rationalistslike Descartes, Spinoza, and Leibnizand
empiricistslike Locke, Berkeley, and Hume. Rationalists place a
strong emphasis on pure reason and metaphysics, suggesting that the
unaided intellect can discover metaphysical truths about the nature
of life and the universe. Empiricists place a strong emphasis on
knowledge gained from experience, confining the intellect to
reasoning about experience based on what it finds in experience.
Kant attempts a synthesis between these two camps by showing that
they are both flawed in a fundamental respect. The empiricists are
wrong to think of experience as consisting only of sensations, and
the rationalists are wrong to think that the intellect can give us
any insight into the essence or nature of things in themselves.
Kant attacks both empiricists and rationalists in this part of the
text.
His main object of criticism in the empiricist camp is Hume, who
Kant nonetheless deeply admiresafter all, Kant's system was
motivated by Hume's skepticism. Hume's mistake, according to Kant,
lies in misunderstanding the nature of experience. Like pretty much
everyone before Kant, Hume believes that experience is
fundamentally a set of simple impressions. Ideas and complex
impressions are built by connecting various simple impressions.
Experience for Hume is what Kant would call "sensations": it is the
simple sense-data of what we see, hear, smell, etc.
Kant criticizes this view by pointing out that experience is
more than just simple impressions that we receive as neutral
observers. Experience comes in an already organized form.
Everything that we can experience happens in space and time. Space
and time, Kant argues, are not impressions or sensations: we do not
learn about them through experience because they are pure
intuitions. Further, everything that happens in space and time is
subject to the law of cause and effect. This law is also not an
impression or a sensation but a pure concept of the understanding.
Pure intuitions and concepts organize experience for us and give it
its form. We are not neutral observers of an objective world; we
actively shape the world we perceive so as to make it
intelligible.
Hume argues that we can have no knowledge of cause and effect
because we cannot find causes or effects in the simple impressions
that constitute the entirety of our experience. Kant agrees that
there are no causes and effects to be found in experience, but
suggests that our understanding applies the concept of causation to
experience in order to make it intelligible. To modify Bertrand
Russell's analogy, we see the world through causation-colored
sunglasses.
If we can dismiss Hume's skeptical empiricism by pointing out
that we can have a priori knowledge of cause and effect, space and
time, we encounter an equally unsavory dogmatism in the rationalist
camp. If synthetic a priori knowledge is possible, then we can
learn substantial truths about the universe that have a necessity
and universality that we cannot find in experience. While
experience can only tell us about appearances, about how things
seem to us through the imperfect medium of the senses, reason can
tell us about things in themselves.
Kant's answer to this temptation is twofold. First, our a priori
pure intuitions and pure concepts only help us to make sense of
appearances. Kant makes no claim that the laws of cause and effect
apply to things in themselves, only that we apply them with
necessity to appearances. Second, our pure intuitions and pure
concepts do not give us any substantial knowledge. All they do is
prescribe the form our experience takes. They are the cup into
which experience is poured, so to speak: we cannot drink the cup,
but without the cup we wouldn't be able to drink at all.
Kant's pure intuitions and pure concepts reconcile the
empiricist and rationalist camps by showing that, on one hand, we
can have a priori knowledge relating to experience and on the other
hand, this a priori knowledge does not tell us anything about
things in themselves. Kant recognizes that we are not passive
recipients of our sensory experience. What we perceive is given its
form by faculties that are innate. These faculties do not tell us
anything about what the world is really like, but they determine
the patterns according to which the world appears to us.
Third Part, Sections 4049
Summary
The Third Part deals with the question, "How is metaphysics in
general possible?" We have seen how both mathematics and pure
natural science are possible, by appealing to our pure intuitions
of time and space and the concepts of our faculty of understanding.
We use our pure intuitions and our faculty of understanding to make
sense of experience, but metaphysics, as its name suggests, deals
with matters that are beyond the realm of experience. It either
deals with concepts that lie outside of experience (like God) or it
deals with the totality of possible experience (like whether the
world has a beginning and an end). Intuition and understanding are
of no use here. Metaphysics deals with the faculty of pure reason,
and the ideas contained therein.
The distinction between the understanding and reason is crucial.
Philosophical error frequently arises from a confusion of one for
the other. Any concept that can be applied to experience belongs to
the faculty of understanding and has nothing to do with
metaphysics. Reason is not directed toward experience, and any
attempt to apply the ideas of reason to experience is mistaken.
Reason tries to make experience complete. Reason tries to tie
all of experience together and to give it meaning. This drive to
metaphysics is not in itself problematic; it becomes wrong-headed
only when we apply our pure intuitions or pure concepts of the
understanding to the pursuit.
Kant distinguishes three different kinds of "ideas of reason"
psychological ideas, cosmological ideas, and the theological
ideathat between them contain all of metaphysics. This summary will
deal with psychological ideas, while the summary of sections 5056
will deal with cosmological and theological ideas.
Psychological ideas try to identify some sort of substance or
ultimate subject underlying all the predicates we can apply to a
subject. For instance, we can describe a cat as "a thing with
claws" or "a thing that purrs" and so on, but what is the "thing"
itself? What do we have left over when we peel away all the
predicates? Kant suggests that this search is futile: the
understanding helps us make sense of experience by applying pure
concepts to empirical intuitions, and concepts take the form of
predicates. The only knowledge we can have comes in the form of
predicates attached to subjects.
A possible candidate for ultimate subject comes in the form of
the thinking ego, or soul. When describing internal states ("I
think," or "I dream," for example), we refer back to an "I" that is
fundamental, indivisible, and unique. However, Kant argues, this
"I" is not a thing or a concept that we can have knowledge of in
itself. That we are capable of experience at all suggests that we
have some sort of consciousness, but we refer to this consciousness
(or soul) without having any substantial knowledge of it.
Just as appearances in the external world suggest to us that
there are things in themselves, so inner sensations suggest to us
that we have some sort of soul or ego. But, just like things in
themselves, we can know nothing about this soul; we can know only
about the appearances that manifest themselves. This conclusion
suggests that Descartes is wrong in thinking we can know about the
mind better than we can know about external bodies.
What we can say about the soul we can say only in reference to
our own experience. Thus, we can't know whether or not the soul is
immortal, since that is to ask questions about the soul outside the
realm of experience.
Commentary
In the Prolegomena, Kant divides mental activity into three
major faculties. First, there is the faculty of sensibility that
uses the pure intuitions of space and time to form our sensations
into empirical intuitions. This faculty helps us organize and make
sense of what we see, hear, smell, touch, and taste. We can also
use the pure intuitions of space and time to reason
mathematically.
Second, there is the faculty of understanding that uses pure
concepts to form our empirical intuitions into appearances. This
faculty allows to make sense of what we see, hear, smell, touch,
and taste as according itself with regular, universal laws of
nature, and so helps us make general inferences and conclusions.
That, effectively, is the business of natural science
Third, Kant introduces us to the faculty of reason in this part
of the text. While the faculties of sensibility and understanding
help us make sense of experience, reason helps us make sense of
purely mental concepts. It does this by means of ideas, which try
to fill out and give completeness to the concepts we apply in
experience. For instance, psychological ideas take the concept of
substance and try to flesh out what it is we mean when we talk
about a "thing." What substance underlies a thing and makes it what
it is? We will see similarly that the cosmological ideas try to
fill out our concept of cause, trying to identify connections that
go beyond those we encounter in experience, and that the
theological idea tries to fill out our concept of community, trying
to identify what unifies everything that exists.
Our faculty of sensibility gives us math, our faculty of
understanding gives us science, and our faculty of reason gives us
metaphysics. The important conclusion to draw from this discussion
of faculties is that metaphysics is the product of pure reason and
deals only with ideas in our head; in other words, metaphysics
cannot tell us about how things are in themselves. Metaphysics as
Kant conceives it is more a matter of untying mental knots than
determining whether or not God exists.
The mental knot Kant associates with psychological ideas is that
of substance, and particularly that of a thinking substance. Talk
of substances was a major preoccupation of the rationalist
metaphysics of the 17th and 18th centuries, and Descartes was one
of the major philosophers to discuss substances. Descartes is
famous for the statement "I think therefore I am": I cannot doubt
that I exist, since the act of doubting is an act of thought and I
couldn't think unless I existed. I exist: but what can I know about
this "I" that I am? While I know that I think, I can doubt that I
have a body (I could be a butterfly dreaming I have this body), so
I conclude that I am a thinking (as opposed to bodily) substance. I
may think I know, or I may guess, any number of things about my
body, but while these thoughts or guesses may be mistaken, I cannot
doubt that I am thinking or guessing. From this line of reasoning,
I conclude that my mind is better known to me than my body.
And so on. In the Meditations, Descartes questions the
reliability of the senses, and then attempts to see how much he can
know about himself and the world around him using only his
intellect.
According to Kant, all I can know about this "I" is that I am.
What I sense and think are representations, and these
representations have to take place within a subject. For things to
be seen and heard there has to be a consciousness that is doing the
seeing and hearing. This "I" essentially represents that logical
necessity: there must be something doing the seeing and hearing,
and I call that something "I."
This "I" is not something I encounter in experience; it is the
basis for my experience. As a result, we cannot apply to it the
categories we apply to experience. Descartes tries to do
essentially that, applying the concept of substance and other
concepts of the pure understanding to it. Kant suggests on the
contrary that we should think of this "I" the way we think of
things in themselves: we can infer that it is, but we cannot infer
anything about it. Pure reason, engaging in metaphysics, cannot
tell us anything substantial about the way things are.
< Previous SectionThird Part, Sections 4049Next Section
>Conclusion
Third Part, Sections 5056
Summary
Kant expresses the cosmological ideas as four distinct
antinomies, or pairs of seemingly contradictory metaphysical
propositions. They are:
(1) The claim that the world has a definite beginning and end
vs. the claim that the world is infinite
(2) The claim that all things are made up of simple,
indestructible, indivisible parts vs. the claim that everything is
composite and infinitely divisible
(3) The claim that we can act in accordance with our own free
will vs. the claim that everything we do is determined by
nature
(4) The claim that there are necessary causes vs. the claim that
nothing is necessary and everything is contingent
None of these claims can be verified in experience, and so we
are tempted to think that they deal not with appearances but with
things in themselves. Reason by itself seems capable of proving
either side of each antinomy. Rather than come down on one side or
the other, Kant proceeds to show how each antinomy results from a
misunderstanding of the matter being discussed.
The mistake in the case of (1) comes from treating space and
time as things in themselves rather than as intuitions of our
faculty of sensibility. Space and time are features of our
experience, and do not exist independently of experience. It makes
no sense to ask whether or not the world has a limit in space and
time, since that limit would exist outside the realm of our
experience.
In (2), when we talk about the parts into which a composite
thing can be divided, we are assuming that these already exist,
waiting inside the composite thing. But these parts are only
appearances, and so cannot have any existence until they are
experienced.
In (3), causal necessity and freedom are made to seem
contradictory when in fact they are compatible. The laws of nature
can only operate within the confines of space and time, and so are
applicable only to appearances. Freedom, on the other hand, is the
ability to outside the confines of causality, and so to exist
outside the confines of experience. Freedom, then, is applicable
only to things in themselves.
Our faculty of reason does not deal with experience, and so we
are free in our capacity as rational beings. This freedom must
express itself only in general maxims that do not depend on causal
influence or particular times and places. In obeying these general
maxims, we still follow regular laws in the world of appearances.
Thus, we can be free and also be subject to the laws of nature.
The seeming contradiction in (4) is similarly resolved if we see
that one half of the proposition talks about things in themselves
and the other half of the proposition talks about appearances. In
the world of appearances, every causal connection may be
contingent, which is to say it could have happened otherwise.
Nonetheless, these appearances might have a necessary connection to
things in themselves.
Kant deals very briefly with the idea of a God. In the Critique
of Pure Reason, he shows at length the flaws in all the supposed
proofs for the existence of God. Here, he simply points out that
any "proof" of God's existence is a purely intellectual exercise,
and cannot lead us to fundamental and substantial conclusions
regarding the nature of experience.
In conclusion, Kant remarks that while there are justifiably
many mysteries regarding what we find in experience, there should
be no insoluble problems in the realm of pure reason. These
problems deal only with reason itself and do not reach beyond our
own minds into experience.
Commentary
The four antinomies Kant presents as "cosmological ideas" are
common topics of metaphysical debate. In each case, Kant applies
his distinction between appearances and things in themselves in
order to resolve the antinomy. In the first two, he shows that both
sides of the antinomy mistake appearances for things in themselves,
and concludes they are both false. In the second two, he shows that
two seemingly contradictory points of view are actually both
acceptable so long as we recognize that one is applied to
appearances and one is applied to things in themselves.
The first antinomy assumes that space and time exist
independently of our experience and asks whether or not they have
any limits. The second antinomy assumes that the objects of our
experience have an independent existence and asks whether or not
they have fundamental, simple parts. In both cases, we are trying
to extend our knowledge of phenomena we've experienced beyond our
experience of them. Kant reminds us that the objects of experience
are mere appearances, and that the space and time in which we
perceive them are constructs of our pure intuition. In other words,
they do not exist beyond our experience of them.
Both these antinomies might seem a little odd in the light of
modern physics. We have found a limit to space and time in the Big
Bang, and we have identified the simple parts of objects in atoms
and the elementary particles that constitute these atoms. Still,
Kant could point out that these discoveries have been made in the
realm of physics, not metaphysics. What we have discovered are the
limits of observable experience, not the limits of things in
themselves. The things in themselves that are the source of these
appearances exist outside the realm of space-time and scientific
observation.
The third antinomy is probably the most interesting, as Kant's
answer to it is his ethical theory in a nutshell. The problem of
free will is an old one, and a favorite topic of philosophical
debate. If we had no free will, we couldn't be held responsible for
what we do: we would be able to excuse our wrongdoings by saying "I
had no choice." Freedom, then, consists in having a choice, in
one's actions not being predetermined by outside forces. However,
nature's laws dictate that every event is caused by some previous
event, and that every event in turn acts as a cause for some
subsequent event. How can we be said to have free will or to act
independently of outside forces, without violating these laws?
Kant's answer is that cause and effect are products of the
faculty of understanding and can be applied only to appearances,
while freedom is a product of the faculty of reason and has nothing
to do with appearances. Because freedom has nothing to do with
appearances, it is outside the boundaries of time and space. As a
result, a free act cannot be contingent on the particularities of
what is happening at a particular time or in a particular place.
Free acts must abide by general maxims. This theory is more fully
explained in Kant's Groundwork for the Metaphysics of Morals, in
which he claims that free acts take the form of a "categorical
imperative" which insists that our actions follow maxims that we
could will as general laws. Freedom does not mean spontaneity; it
means obeying our own law. Because our freedom manifests itself in
an orderly, law-like manner, it does not violate the laws of nature
that apply to all appearances.
The fourth antinomy deals with necessity and contingency. The
question is whether things necessarily happen the way they happen
or whether they might have happened otherwise. To reconcile this
antinomy, Kant identifies two different kinds of causation: a
contingent one that determines how causes work in the world of
appearances, and a necessary one that determines how things in
themselves cause the appearances we experience.
Kant talks here about things in themselves as acting as causes
and as being necessary, but both necessity and cause are pure
concepts of the understanding, and are thus applicable only to
appearances. Kant could excuse himself by saying he does not use
terms like "cause" and "necessary" literally, but simply for lack
of a better expression. Language can only describe the world of
appearances, and when dealing with things in themselves it is
inadequate.
Kant's discussion of the idea of God is very brief, mostly
because his reasoning doesn't change: ideas of reason can only help
us sort things out in our heads, but they can't tell us anything
substantial about the world outside our heads.
Conclusion
Summary
In the Third Part, Kant discusses the various ideas of reason,
and how they mislead the understanding into posing insoluble
metaphysical questions. In this section, he hopes to determine the
value of reason and the precise bounds within which it can operate.
While we can never know more about an object than what experience
teaches us, the concepts of our understanding help us to pose
metaphysical questions that experience cannot answer. It is only
natural, then, that we should consult reason when experience lets
us down.
Kant distinguishes metaphysics from mathematics and science by
saying that the former has bounds while the latter two have only
limits. Both math and science are complete in and of themselves:
there are no insoluble problems in these fields, no questions that
cannot be answered given enough time, insight, and progress. They
are limited only in that their scope is not absolutely general.
Math cannot answer metaphysical or moral questions, and science
cannot give us insight into things in themselves. However, morality
and metaphysics are not needed in mathematical explanations and the
nature of things in themselves does not affect the progress of
science, which deals only with the objects of experience. What
these fields don't know can't hurt them.
Metaphysics, on the other hand, is bounded: reason poses
questions for itself that it cannot answer. In investigating
metaphysical questions, reason bumps up against boundaries that it
cannot press beyond. That is, metaphysics asks questions about the
nature of things in themselves, but we cannot gain definite
knowledge of anything outside experience.
However, these bounds can be useful. While we cannot know what
is beyond them, we can infer from the existence of these bounds
that there is something beyond them (i.e. things in themselves) and
we can infer the connection these things in themselves must have
with the perceptible world. While we cannot reach beyond experience
to things in themselves, we can examine the relation between things
in themselves and our experience.
Kant has already dismissed any attempt to prove the existence of
God or to learn anything positive about God's nature. Our knowledge
is structured by categories and concepts that are applicable only
to experience, so we cannot apply these categories and concepts in
any meaningful way to things beyond experience. For instance, it
would be a mistake to attribute supreme rational powers to a
Supreme Being, since we can't attribute anything to something
beyond experience. What we can do, however, is attribute the
rational order of the experienced world to a Supreme Being that
sits outside the experienced world. This is not to say anything
about a Supreme Being, but only about the relation that Being has
with the world. If we see the world as structured in a rational
way, we find a unity in experience by stretching our powers of
reason right to the bounds of experience.
Though there is no way of knowing the reason why we have reason,
Kant offers some speculation. He suggests that perhaps reason, in
showing us the bounds of experience, also teaches us that there is
something beyond experience that we cannot know, thereby giving us
a more balanced perspective. Without the idea of a soul, we might
think psychology can fully explain human behavior; without the
cosmological ideas, we might think nature is sufficient unto
itself; without the idea of God, we might become fatalists,
doubting the possibility of free will.
Commentary
In the Third Part, Kant dismisses standard metaphysical
questions and debates as pointless. He argues that these questions
arise from a failure to distinguish between appearances and things
in themselves, and from trying to apply the concepts of the
understanding to something other than the objects of experience. In
this conclusion, he shows us that reason and metaphysics do in fact
have a very important valuejust not the value we normally think of
them as having.
The distinction between math and science on the one hand, and
metaphysics on the other, rests on the important distinction Kant
makes between limits and bounds. Math and science are limited,
meaning that they cannot tell us everything. No mathematical
equation can tell me whether cloning is wrong, and no scientific
experiment can tell me whether or not God exists. (These limits,
incidentally, become all the more important in an age when
scientific advances pose increasingly complicated moral dilemmas.)
However, there is no boundary to what math or science can solve
within their particular realms. This is not to say we have solved
or can solve all the problems in these fields, but just to say that
there is no external constraint on what can be learned. There may
be puzzles we will never solve, but they will nonetheless have
solutionsjust solutions we are incapable of finding. Neither math
nor science will ever confront us with a puzzle to which there is
no solution.
While math and science are limited, metaphysics is bounded. That
means that there are metaphysical puzzles to which there is no
solution. The ideas of reason deal with precisely that. "What is
the nature of the soul?" is a question, says Kant, to which we
cannot give an answernot because we do not know the answer, but
because there is no answer to give. Metaphysics tries to deal with
things in themselves, but all our concepts and intuitions are
suited only to dealing with appearances. Our reason poses riddles
for us for which there is no answer. Metaphysics is an attempt to
reach for things that are beyond our grasp.
If metaphysics is bounded in such a way that we can never answer
any of the questions it poses, we might think of it as a useless
discipline. Kant suggests, on the contrary, that its value lies
precisely in the establishment of these bounds. We cannot know what
is beyond experience, but in reaching for it, we know there is
something beyond experience. If something is bounded, that suggests
there is something outside those bounds. Limits do not teach us
this.
If all we had were our faculties of sensibility and
understanding without reason, and all we had was math and science
without metaphysics, we would have no awareness of things in
themselves. We would pursue math and science with the assumption
that we were learning everything there is to learn. We would assume
that the concepts of science can explain all natural phenomena, and
that whatever science can't explain doesn't exist. For instance, we
would assume that a mind is nothing more than a brain, and that
thought is nothing more than the firing of neurons.
Though reason cannot teach us anything about things in
themselves, it gives us an awareness that there are things in
themselves, and thus gives us an awareness of the bounds placed
upon our learning. Metaphysics is important to us precisely because
it is bounded. It gives us perspective, something that none of the
more complete sciences can give us. While math and science teach us
what we can know, metaphysics teaches us what we can't know.
Solution
Summary
The metaphysics of previous generations, which Kant discusses in
the Third Part, is dialectical nonsense: debates as to the nature
of the soul or the possibility of freedom can go on and on and back
and forth forever without reaching any satisfying conclusions. He
cannot deny that metaphysics exists as a disposition of human
reason (we are naturally drawn to metaphysical questions), but he
does deny that metaphysics as it has been conducted can lead to any
real knowledge.
Kant is now finally ready to answer what he posed as the general
question of this book: "How is metaphysics possible as a science?"
His answer, effectively, is one word: "critique." Our faculty of
reason cannot teach us anything about what lies beyond experience
or about things in themselves, but it can help us to categorize and
classify the various concepts of our faculties of sensibility,
understanding, and reason. Rather than use reason to look outward,
we should turn it inward and direct it toward itself.
Kant considers science to be a body of synthetic a priori
knowledge. The faculty of reason has no power to gain a priori
knowledge of things outside experience, or even outside the
intellect. What it can do is survey the mind in its entirety and
gain knowledge a priori about the nature and variety of our many
concepts and faculties.
Kant is confident that anyone who has read the Prolegomena will
conclude with him that nothing to date has advanced metaphysics in
the slightest, and that metaphysics as it has been conducted to
date is useless. Nevertheless, Kant remarks, we are naturally drawn
to metaphysics and cannot just abandon it. For this reason, he
expects formerly dogmatic metaphysicians to begin advancing the
critical philosophy he envisions with great vigor.
Kant challenges anyone who disagrees with his dismissal of
dogmatic metaphysics to provide one example of a metaphysical
synthetic a priori judgment that has been proved with certainty.
Such a judgment cannot be based on probability or conjecture, since
a priori truths are necessary, and it cannot be based on common
sense, since we derive common sense from experience. While common
sense is useful for practical purposes, it cannot advance
metaphysics as a science.
Commentary
Kant uses the term "metaphysics" to talk about two very
different things. On one hand, he talks about the "dogmatic"
metaphysics that he attributes to his rationalist predecessors, and
on the other hand, he talks about the critical metaphysics he
intends to set up in its place. In examining this distinction, we
should also get a clearer sense of what a "critique" is, and why
Kant thinks "dogmatic" metaphysics is not a science but that his
critical metaphysics is.
"Dogmatic" metaphysics pursues the kinds of questions outlined
in the Third Part as prompted by ideas of reason. These questions
ask about the nature of the soul, the possibility of freedom, the
ultimate constituents of matter, the existence of God, and so on.
Metaphysics relies entirely on the faculty of reason, and Kant
tries to show us that reason cannot get us any closer to answering
these questions. The faculty of reason cannot connect with anything
outside the mind, and certainly not with things in themselves.
If we recall, a science is a body of synthetic a priori
knowledge. That is, it is a field of study that makes interesting,
non- analytic judgments, but does so without any reference to
experience. In order to make synthetic judgments without reference
to experience, our mental faculties must be able to make
significant connections within their own pure concepts. Our faculty
of sensibility can use its pure intuitions of space and time to
make mathematics and geometry. Our faculty of understanding can use
its pure concepts to make natural science possible. Our faculty of
reason has ideas, so the pressing question is what kind of
synthetic judgments can these ideas produce?
We have seen that the ideas of reason pose all sorts of
metaphysical questions that reason cannot answer. We have also seen
that in doing so, reason pushes itself to the bounds of human
knowledge, giving a sense of completeness and unity as to what we
can know. Reason, then, has a sense of what kind of knowledge is
possible, and so is ideally suited to examining the different
mental faculties and determining precisely how knowledge is
structured. The Prolegomena itself has essentially employed this
technique: throughout, Kant has been investigating the different
kinds of knowledge we have and the grounds on which this knowledge
is justified. His conclusions that there are three mental faculties
(sensibility, understanding, and reason), that the faculty of
sensibility contains pure intuitions of time and space, or that the
faculty of understanding is structured according to the concepts
listed in his table of categories, are all conclusions reached
through a critical investigation of the structure of knowledge.
While "dogmatic" metaphysics asks what we can know, Kant's
critical metaphysics asks how we can know. A "critique" is an
investigation that looks inward rather than outward, that
investigates knowledge itself rather than the objects of knowledge.
The Prolegomena is a shortened version of Kant's great work, the
Critique of Pure Reason, which is an attempt to investigate how and
what our faculty of reason is capable of.
Kant is not doing psychology. He is not trying to figure out how
the mind works or anything like that. Rather, he is trying to
figure out how knowledge works, and any claims he makes about the
workings of the mind are based on his conclusions as to how
knowledge must be structured in the mind.
One of the most significant conclusions of Kant's critical
philosophy is that many concepts we think of as objectivelike
space, time, or causationare in fact part of the way we structure
knowledge. These concepts, as Kant shows in the Third Part, are
often the source of perplexing metaphysical conundrums. In showing
that these concepts are not to be found in the world, but rather in
our own faculties, Kant is essentially redirecting metaphysics. He
is telling us that we should not apply metaphysical concepts to the
world but to our own faculties. All metaphysics can do for us is
tell us how we know what we know. It cannot tell us what we cannot
know.
Appendices
Summary
Kant takes it as self-evident that it is in everyone's interests
to establish metaphysics as a science that proceeds according to
agreed-upon and well- grounded principles. Kant's work proposes to
do just that, so he feels he is only open to criticism if he has
failed to do so, or if he is mistaken in claiming that metaphysics
until now has been unproductive. If someone wishes to make the
latter accusation, he challenges them to show him one metaphysical
truth that is grounded with certainty and agreed upon by all.
The second, and longest, appendix deals primarily with an
unfavorable review of Kant's Critique of Pure Reason published in a
journal of metaphysics. The reviewer dismisses Kant's work as
unclear and unoriginal metaphysical idealism. He makes no mention
of Kant's central project of trying to make metaphysics scientific,
and does not once refer to Kant's important category of the
synthetic a priori. Though this reviewer clearly misunderstood Kant
entirely, Kant takes this opportunity to clarify what he means by
"transcendental" or "critical" idealism.
Traditional idealists, like Berkeley, assert that all the
objects of experience are illusory, and that only pure concepts
contain truth. Berkeley claims we have only a posteriori knowledge
of space and all the objects in it, and that we therefore cannot be
certain of this knowledge. Kant, on the other hand, asserts that we
can know about space and time a priori, and that we can have
certainty with regard to our experience. Contrary to Berkeley, Kant
asserts that our pure concepts are illusory and that only
experience contains truth.
Kant's motive for writing his Critique of Pure Reason was that
there is no standard for agreement on judgments in metaphysics.
This being the case, he does not feel his reviewer's judgment has
any solid basis. He challenges his reviewer to produce one
metaphysical synthetic a priori principle that can be used to
contradict what Kant has written. Better yet, he offers his
reviewer the choice of any one of the eight metaphysical
propositions listed in his discussion of cosmological ideas. Kant
wagers that he could provide a "proof" of the contrary position
that his reviewer would not be able to dislodge. He suggests
further that he could then provide a similar "proof" of the
reviewer's own position, in order to show what dire straits
metaphysics stands in.
If people acknowledge the problems in contemporary metaphysics,
and study his work as a possible alternative, Kant is confident
that much headway can be made, not only in metaphysics, but in
other fields as well. For instance, it could free theology from
dogmatism and speculation, as well as from the shallow mysticism
that masks itself with dogmatic metaphysics.
Commentary
Kant's Critique of Pure Reason was met mostly with bewilderment
when it was first published in 1781. The Prolegomena, published in
1783, was primarily intended to clarify and simplify what was said
in the Critique in order to make it accessible. A second, largely
revised, edition of the Critique was published in 1787.
Readers and reviewers generally failed to appreciate the
originality of Kant's ideas. Readers interpreted Kant as saying
something more familiar to them than what he was actually saying.
The idea that rationalist metaphysics, which was the main
occupation of philosophers in Germany at the time, could be
dismissed entirely was too revolutionary a concept to catch on
easily.
One of Kant's main troubles, it seems, was that he was taken for
an idealist. Idealism is the doctrine that reality is dependent
upon the mind. A common idealistic argument suggests that
everything I know about the world I learn through the senses, and
so the things I "know" are not external objects and phenomena, but
just the report of my senses. My concept of the world, an idealist
would argue, is based entirely on sensory images that exist only in
my mind, and has at best a dubious connection with the things in
themselves that exist in the world.
A famous proponent of this position is George Berkeley, an Irish
bishop who argues that esse est percipi"being is being perceived."
He asserts that chairs and tables and the like have no independent
existence, that they only exist in the mind of someone who is
perceiving them. He evades the odd claim that these things cease to
exist when no one is perceiving them by positing the existence of
God as a being who is perpetually perceiving everything.
Kant's philosophy is very firm in asserting that we can know
only about appearances, and that we can know nothing about things
in themselves. This assertion is enough to make Kant an idealist of
sorts, but he wants to qualify this title of "idealism." He is not,
like Berkeley, saying that only appearances exist: though we can
know nothing about things in themselves, they are still a crucial
part of his philosophy.
Kant calls his philosophy "transcendental" or "critical"
idealism. The "transcendent" world of things in themselves is
contrasted with the "immanent" world of appearances. Because he
believes that things in themselves exist, his idealism believes in
the existence of a "transcendent" world that is behind the world of
appearances.
His idealism is "critical" because it is directed toward what we
can know, not toward what exists. He is not saying that only
appearances exist, but that appearances are all we can know. Kant's
critical philosophy questions how we can come to know what we know,
so he is an idealist only in saying that we cannot know things in
themselves.
The concept of the thing in itself is one of the most
controversial aspects of Kant's philosophy. In Germany, Kant's
successorsmost notably Hegelcriticized this concept, and advanced a
pure form of idealism that did away with things in themselves
entirely. It is unclear what sort of relation things in themselves
are supposed to bear to appearances if categories such as space,
time, and causality do not apply to them. For instance, suppose we
see Frank hit John, and then John hit Frank back, we must assume
that these appearances are somehow related to things in themselves.
But how can there be actions and reactions in things in themselves
without the concept of time?
Because he says that they are unknowable, Kant cannot say
anything about the nature of things in themselves, but his silence
in this regard leaves us with a number of mystifying puzzles. How
can appearances in space and time be related to things in
themselves outside of space and time? Those who are dissatisfied
with Kant generally identify their dissatisfaction with the
unanswered questions raised by Kant's doctrine of things in
themselves. Idealists generally deny that things in themselves
exist, and realists generally assert that categories like space and
time have more than just a subjective existence.
Kant's Tables of Categories
Logical Table of Judgments
1: As to Quantity Universal [all x are y] Particular [some x are
y] Singular [the x is y] 2: As to Quality Affirmative [the x is a
y] Negative [the x is not a y] Infinite [the x is a non-y] 3: As to
Relation Categorical [x is y] Hypothetical [if x then y]
Disjunctive [either x or y] 4: As to Modality Problematic [x is
possibly y] Assertoric [x is y] Apodeictic [x is necessarily y]
Transcendental Table of the Concepts of the Understanding
1: As to Quantity Unity (Measure) Plurality (Quantity) Totality
(Whole) 2: As to Quality Reality Negation LimitatioN 3: As to
Relation Substance Cause Community 4: As to Modality Possibility
Existence Necessity/VERSE
Pure Physiological Table of the Universal Principles of Natural
Science
1: Axioms of Intuition 2: Anticipations of Perception 3:
Analogies of Experience 4: Postulates of Empirical Thought in
General
< Previous SectionKant's Tables of CategoriesNext Section
>Study Questions
Analytical Overview
Kant's philosophy has been called a synthesis of rationalism and
empiricism. From rationalism he takes the idea that we can have a
priori knowledge of significant truths, but rejects the idea that
we can have a priori metaphysical knowledge about the nature of
things in themselves, God, or the soul. From empiricism he takes
the idea that knowledge is essentially knowledge of experience, but
rejects the idea that we cannot learn any necessary truths about
experience, and in doing so he rejects Hume's skepticism.
He is able to create this synthesis largely thanks to a radical
reconception of the nature of knowledge that comes from from
experience. Though empiricists and rationalists may have disagreed
about the value or certainty of knowledge from experience, they
both generally thought of the mind as a neutral receptor: knowledge
from experience was simply the report of the senses. Kant points
out that our knowledge of experience extends far beyond what the
senses can report. Our senses can report sensations, but they
cannot give these sensations a structure in space and time, or
organize them according to cause and effect. According to Kant, our
faculties or sensibility and understanding are largely responsible
for what we think of as "knowledge from experience."
By giving our mind this complex internal structure, Kant makes
room for a great deal of a priori knowledge. Though the sensations
that are the basis for all our experience come from things in
themselves, any regularity or structure we find in these sensations
comes from our mental concepts. Thus, while Kant does not slip into
the idealist position of saying that reality is all a matter of
perception, he does claim that the laws of nature are the laws of
our mental faculties. For something to be an objective law, it must
be synthetic and it must be a priori, and Kant identifies the
possibility of synthetic a priori knowledge within the structure of
our mental faculties.
If our sense of order and regularity is not something we find in
experience, but something we impose upon experience, the study of
this order and regularity is a study of our own faculties rather
than a study of experience. Kant reconceives the purpose of
metaphysics as being one of critique: we must seek to understand
how knowledge is structured, and consequently how the various
concepts of our mental faculties are organized. This is an
important step for philosophy: after Kant published his work, there
was been less interest in making extravagant claims about the
nature of the universe, and greater emphasis on determining what we
can know and on what grounds we can claim to know it.
This kind of scrutiny, which Kant advocates, has led to some
serious attacks on his work. The German Idealistsnotably Hegelwere
the first to call into question Kant's concept of the thing in
itself. Kant insists that while all we can perceive are
appearances, these appearances are caused by things in themselves
that are outside the realm of experience. Because they are outside
the realm of experience, they are also outside the realm of space
and time and any of the regularities we perceive in nature. A
number of questions can be raised about what kind of relation
things in themselves can have with appearances if categories such
as time, causation, and even existence do not apply to them. The
response of the German Idealists was to abandon the concept of
things in themselves and assert that only appearances exist.
Analytic philosophy also got its start by criticizing Kant. This
movement criticized in particular his category of the synthetic a
priori. Frege was the first to point out that geometry is not
synthetic a priori. Pure geometrywhich consists only of deductive
inferencesis analytic, and empirical geometrywhich deals with what
space is like in the real worldis known a posteriori. This position
was given a boost by Einstein's relativity, which shows that space
is very different from what we had assumed and our understanding of
it is certainly not a priori.
Frege also complains that Kant's definition of analytic and
synthetic judgments rests on the subject-predicate form of grammar,
which is not a necessary part of the logical structure of language.
Efforts to define and classify analytic and synthetic judgments
have been a major pre-occupation of analytic philosophy, especially
in the first half of the twentieth century.
Though many of Kant's doctrines have fallen into question, his
exhortation toward critical philosophy remains with us. Perhaps his
most lasting contribution is the setting up of a new standard for
rigor and circumspection in philosophical investigations.
Study Questions
Kant claims in the preface that Hume interrupted his "dogmatic
slumber." What was Kant's "dogmatic slumber" and how did Hume's
attack on causal reasoning prompt Kant's critical philosophy?
Answer for Study Question 1 >>
Kant's philosophical development took place in the German
tradition of rationalist metaphysics. In the Prolegomena, as in
other of his mature works, Kant refers to this form of metaphysics
as "dogmatic" because there is very little effort made to question
the ground on which these metaphysical claims are justified. Hume
awoke Kant from this "dogmatic slumber" (which is what Kant calls
his metaphysical period in the preface) by showing the importance
and the difficulty of justifying knowledge claims. Hume argues that
we have no rational justification for believing that every effect
has a cause, but that we simply believe this out of habit. Kant
observes that Hume's reasoning could be applied generally to a
priori knowledge, thus casting doubt on the rational justification
of all metaphysics. Hume's skepticism prompts Kant to seek a more
solid basis on which to ground metaphysics.
Close
What is the difference between the a priori/a posteriori
distinction and the analytic/synthetic distinction? How do both of
these distinctions differ from the distinction between necessary
and contingent truths?
Answer for Study Question 2 >>
The a priori/a posteriori distinction has to do with cognitions,
or things that we know. It distinguishes between knowledge I can
have prior to any experience and knowledge I gain from experience.
The analytic/synthetic distinction has to do with judgments. It
distinguishes between judgments that are trivial and judgments that
bring together two different concepts. The necessary/contingent
distinction has to do with whether a certain fact could have been
otherwise. A priori truths are generally considered necessary,
since they do not seem to hinge on the particularities of
experience. However, saying a truth is a priori is a matter of
discussing how we know it, and saying it is necessary is a matter
of discussing its relation to other truths and to the world.
Close
What is a "thing in itself"? Why can't we perceive it directly?
How can we perceive it? How can we even know that things in
themselves exist if we cannot perceive them?
Answer for Study Question 3 >>
Kant argues that while experience is made up entirely of
appearances, these appearances are in some way caused by things in
themselves. We cannot perceive things in themselves directly; what
we perceive must first be interpreted by our senses, and then by
our faculties of sensibility and understanding. Our senses and
faculties are what make it possible to connect with the world
outside our mind, but they also determine the way this connection
is made. Though we cannot perceive things in themselves directly,
we know they must exist because there must be some cause behind the
appearances we meet with in experience. The existence of things in
themselves is crucial to Kant's philosophy, but he insists that we
cannot know anything about them.
Close
What is the difference between judgments of perception and
judgments of experience? What is the significance of this
distinction?
What is Kant's criticism of Hume? Based on your knowledge of
Hume, do you think this criticism is correct?
What is the purpose of our faculty of reason? What can it do?
What can't it do?
What is the source of the "antinomies" discussed as cosmological
ideas? How are these antinomies resolved?
What is the distinction between limits and bounds? What is the
significance in saying that math and science have limits and
metaphysics has bounds?
What is a "critique"? What is the solution to the general
question of the Prolegomena? How is it a solution?
In what way is Kant's "transcendental" idealism dependent on
things in themselves? What problems are there with the doctrine of
things in themselves? How might Kant defend this doctrine?
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This SparkNote
Terms
Metaphysics - The field of philosophy that investigates the
constitution, nature, and structure of reality. Metaphysics goes
beyond physics to examine the reality behind the phenomenal world.
It asks questions that cannot be verified in experience: "Does God
exist?" "Is the soul immortal?" "What are the ultimate constituents
of matter?" "How are mind and matter connected?" and so on. In the
Prolegomena, Kant argues that this kind of "dogmatic" metaphysics
can never arrive at satisfying answers because our faculty of
reason cannot teach us anything about things in themselves. He
tries to replace dogmatic metaphysics with his own critical
metaphysics that sets about examining the constitution, nature, and
structure of knowledge.
Analytic - A statement whose predicate concept is contained in
its subject concept. An example is "all bachelors are unmarried."
The concept of being unmarried is part of the concept of
"bachelor," so the predicate does not say anything new. Instead, it
offers an analysis of a part of the concept of the subject.
Synthetic - A statement whose predicate concept is different
from its subject concept. Such a statement joins two different
concepts together, and in doing so, produces new and interesting
judgments. The Prolegomena makes much of synthetic judgments that
can be known a priori, since they constitute mathematics, pure
natural science, and metaphysics.
a priori - Knowledge that can be gained prior to any experience.
Mathematics is a form of a priori knowledge, because we can sort
out mathematical truths in our head. Kant also refers to a priori
cognitions as necessary, since nothing in experience can possibly
contradict them. Synthetic a priori judgments are thus important,
since they are necessary and interesting truths that we can know
prior to any experience.
a posteriori - In contrast with a priori cognitions, a
posteriori cognitions consist of knowledge that we gain from
experience. These generally have to do with facts about objects in
the world, like "all swans are white."
Intuition - A translation of the German word Anschauung, this
word means more exactly a perspective or a point of view. According
to Kant, our faculty of sensibility is structured by intuitions.
There are two kinds of intuition: pure and empirical intuitions.
Our pure intuitions are our concepts of space and time that we
apply to everything we perceive. Once we have applied our pure
intuitions of space and time to sensations they become empirical
intuitions, that is, sensations that exist in space and time. Kant
argues that our pure intuitions of space and time can be exercised
independent of experience, and serve as the basis for mathematics
and geometry.
Concept of the understanding - These concepts, listed in Kant's
table of categories, give a law-like structure to experience. While
the empirical intuitions of our faculty of sensibility give us only
subjective knowledge of experience, the faculty of understanding
makes our empirical intuitions objective by applying to them
universal concepts such as cause and substance. On their own, these
concepts in their pure form serve as the basis for the general laws
of pure natural science, such as "every effect has a cause."
Sensibility - The faculty that gives structure to the report of
our senses. Our senses perceive things in themselves, and our
faculty of sensibility applies our pure intuitions of space and
time to give form to these sensations. Sensations combined with
pure intuition makes empirical intuitions. The faculty of
sensibility ensures that whatever we perceive we perceive in space
and time.
Understanding - The faculty that gives an objective, law-like
structure to our experience. Our faculty of sensibility gives us
empirical intuitions, and our faculty of understanding applies to
these intuitions the pure con