Introduction to Philosophy Evaluating Arguments Thought Experiments References Introduction to Philosophy Logic and Thought Experiments Carnegie Mellon University 9th September 2015
Introductionto Philosophy
EvaluatingArguments
ThoughtExperiments
References Introduction to PhilosophyLogic and Thought Experiments
Carnegie Mellon University
9th September 2015
Introductionto Philosophy
EvaluatingArguments
ThoughtExperiments
References
Writing Assignments and Readings
In this course we’re going to be doing a lot of reading. As perthe syllabus, you should be sure to complete the readingassigned before class on the day that it is due
The writing assignments ask you questions about the readingset on Monday and Wednesday, so you need to make sure to dothe reading to do well on the writing assignments
Introductionto Philosophy
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ThoughtExperiments
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Lecture Notes
The slides from lectures are posted online. Go to the “CourseContent” tab on Blackboard and you’ll see a folder for themthere.
Introductionto Philosophy
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ThoughtExperiments
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Aims for Today
To learn some important tools philosophers use:
1 Logic (used to evaluate arguments)
2 Thought experiments (used for all kinds of purposes!)
Introductionto Philosophy
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Evaluating Arguments
Introductionto Philosophy
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ThoughtExperiments
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Terminology
In philosophy we care about arguments that can be given infavor of a position (more so than the position itself)
1 All raptors are terrifying
2 Blue is a raptor
3 Blue is terrifying
(1)–(2) are premises
(3) is the conclusion
Introductionto Philosophy
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ThoughtExperiments
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Validity
When we say that an argument is valid we mean . . .
. . . that if its premises were true then its conclusion wouldhave to be true (Perry et al., 2015, 9)
Introductionto Philosophy
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Validity
1 All raptors are terrifying
2 Blue is a raptor
3 Blue is terrifying
This is a valid argument. If the premises are true, then theconclusion must be true.
Introductionto Philosophy
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Check Your Understanding
Take 30 seconds (or less) to think about this question:
Can a valid argument have a false conclusion?
Introductionto Philosophy
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Check Your Understanding
Can a valid argument have a false conclusion?
Yes!
1 All English prime ministers are squirrels
2 David Cameron is an English prime minister
3 David Cameron is a squirrel
If the premises were true then the conclusion would also haveto be true. But David Cameron is not a squirrel!
Introductionto Philosophy
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ThoughtExperiments
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Check Your Understanding
Take 30 seconds (or less) to think about this question:
Can an invalid argument have a true conclusion?
Introductionto Philosophy
EvaluatingArguments
ThoughtExperiments
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Check Your Understanding
Can an invalid argument have a true conclusion?
Yes!
1 If Becky can vote then Becky is a US citizen
2 Becky cannot vote
3 Becky is not a US citizen
This is an invalid argument (do you remember what fallacy it isan instance of?) but the conclusion is true-I am not a UScitizen!
Introductionto Philosophy
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ThoughtExperiments
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Soundness
When we say that an argument is sound we mean . . .
. . . that it is valid and has all true premises (Perry et al.,2015, 9)
An unsound argument is either invalid, or is valid but has atleast one false premise
Introductionto Philosophy
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Soundness
Example of a sound argument:
1 Every integer > 1 is either prime or the product of primefactors
2 5987 is an integer > 1
3 5987 is either prime or the product of prime factors
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More Terminology
Sometimes arguments can fail to be valid (and thus fail to besound) but should not be dismissed as “bad” arguments
For example:
1 90% of visitors to Wikipedia only view content (i.e. theydon’t edit or create new material)
2 Jenny is a visitor to Wikipedia
3 Jenny only views content (and doesn’t edit or create newmaterial)
Arguments like the one above are said to be strong
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Strength
When we call an argument strong we mean that it is invalid,but if all of its premises were true, then its conclusionwould probably be true
Strength can come in degrees
An invalid argument that is not strong is said to be weak
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Weakness
Here’s an example of a weak argument:
1 10% of visitors to Wikipedia create or edit material
2 Jenny is a visitor to Wikipedia
3 Jenny creates or edits material
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Cogency
We call an invalid argument cogent if it is strong and has alltrue premises
For example:
1 82% of Americans between the ages of 18 and 34 haveinternet access
2 Miley Cyrus is an American between the ages of 18 and 34
3 Miley Cyrus has internet access
Introductionto Philosophy
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Cogency
Here’s an example of an invalid argument that is not cogent:
1 82% of Americans between the ages of 18 and 34 haveinternet access
2 Madonna is an American between the ages of 18 and 34
3 Madonna has internet access
Why does it fail to be cogent?
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Summary
When asked to evaluate an argument, keep these concepts inmind:
1 Validity
2 Soundness
3 Strength
4 Cogency
Introductionto Philosophy
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Thought Experiments
Introductionto Philosophy
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Thought Experiments
The runaway train scenarios we discussed last week wereexamples of thought experiments
When we conduct a thought experiment, we are engaging inhypothetical thinking
In the runaway train scenarios, we were trying to figure out the“right” thing to do
We also tried to figure out why most people thought the rightthing to do was pull the lever, but not to push the fat man
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Thought Experiments
Philosophers are not the only people who make use of thoughtexperiments!
Scientists, such as Galileo and even Einstein, made use ofthought experiments in their work
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The Infinitude of the Universe
Lucretius (who was a first century BC poet) tried to show thatthe Universe is infinite by using the following thoughtexperiment:
Suppose that the Universe has a boundary. Then we can throwa spear at the boundary. If the spear passes through the“boundary”, then it isn’t a real boundary. If the spear stops orbounces back at us, then there must be something on the otherside (in space) that is causing this. Thus, again, the“boundary” is not a real boundary. Consequently there is noboundary to the Universe and so it must be infinite.
Briefly discuss the above thought experiment with yourneighbor? Do you agree with Lucretius? Why or why not?
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The Infinitude of the Universe?Lucretius’s thought experiment does not establish theconclusion he hoped it would!
We now know that there are spaces which are finite butunbounded
Simple example: a circle. If we move around the circumferencewe find no “edges” but it is a finite space
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Moral of the Story
Lucretius’s example shows us that while thought experimentscan be powerful, they can also go wrong!
Some questions to ask when you’re presented with a thoughtexperiment:
• Does it make sense?
• Do we need additional info to draw a conclusion? If so,what info?
• What does the author use it to conclude? Can youreconstruct their argument? Is their argument “good”?
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The Experience Machine
Suppose that there were an experience machine that wouldgive you any experience you desired. Super-duperneuropsychologists could stimulate your brain so that youwould think and feel you were writing a great novel, ormaking a friend, or reading an interesting book. All thetime you would be floating in a tank, with electrodesattached to your brain. Should you plug into this machinefor life, preprogramming your life experiences? [...] Ofcourse, while in the tank you won’t know you’re there;you’ll think that it’s all actually happening . . . (Nozick,1974)
Spend a few minutes discussing whether you would plug in(and more importantly, why or why not!) with your neighbor
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Pleasure
We can try to use the experience machine thought experimentto argue against the claim that pleasure is the only thing thatmatters
1 If pleasure is the only thing that matters, then we wouldwant to plug into the experience machine
2 We do not want to plug into the experience machine
3 Pleasure is not the only thing that matters
Together with your neighbor, think about the followingquestions: Do you agree with the conclusion? If so, what otherthings do you think matter? If not, how would you criticize theargument?
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Other Thought Experiments
The Missing Shade of Blue: You’ve not seen a particular shadeof blue, but you’ve seen shades slightly darker and slightlylighter. Can you imagine the missing shade in between?
Memory Swap: Imagine you and your neighbor swappedmemories. Who would be who?
Duplicate People: Two exact duplicates of Captain Sisko arecreated by DS9’s transporter instead of just one. Are they bothCaptain Sisko? Is one the “real” Sisko? Are neither the “real”Sisko?
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Exit Ticket
Select one of the thought experiments that we discussed todayand say what you would conclude from it.
Please give a brief description of the thought experiment so weknow which one you mean (e.g. “the one where you have todecide whether to “plug in” to a machine that gives youpleasurable experiences”)
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Bibliography
R. Nozick. Anarchy, State, and Utopia. Basic Books, 1974.
J. Perry, M. Bratman, and J. Fischer. Logical toolkit. InJ. Perry, M. Bratman, and J. Fischer, editors, Introductionto Philosophy: Classical and Contemporary Issues, pages8–13. 2015.