8/13/2019 Lect11 Realism
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8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
A statement of scientific realism
Characterization (Scientific realism)
Science aims to give us, in its theories, a literally true story of whatthe world is like; and acceptance of a scientific theory involves thebelief that it is true. (van Fraassen, 1066)
Characterization (Common sense realism naturalized)
We all inhabit a common reality, which has a structure that existsindependently of what people think and say about it, except insofar asreality is comprised of thoughts, theories, and other symbols, andexcept insofar as reality is dependent on thoughts, theories, and othersymbols in ways that might be uncovered by science.(Godfrey-Smith, 176)
Common sense realism is part of scientific realism, but it may or
may not be part ofscientific antirealism.Christian Wthrich Topic 11
8/13/2019 Lect11 Realism
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8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
Antirealist strategy in the face of NMA
empirical adequacy orinstrumentalsuccess are sufficient toaccount for the success of science
reason: scientific theories areconstructedto be empirically
adequate/instrumentally successful
by having to deal with anomalies of predecessor theory, latertheories must be more empirically adequate/instrumentallysuccessful
Darwinian selection guarantees that later theories are fitterthan their predecessors in exactly these respects
no need to invoke truth of theories
Christian Wthrich Topic 11
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
Bas van Fraassen: constructive empiricism
The Scientific Image(1980)
instrumentalist in sense of
Godfrey-Smith: scientific theories aredevices to deal with experience
notinstrumentalist in van Fraassensown sense that scientific statementsare not capable of being true/false,
language of science is not beconstrued literally
Christian Wthrich Topic 11
S i ifi li d h i l
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
Characterization (Constructive empiricism)
Science aims to give us theories which are empirically adequate;and acceptance of a theory involves as belief only that it is empiricallyadequate. (van Fraassen, 1069)
Characterization (Empirical adequacy)[A] theory is empirically adequate exactly if what it says about theobservable things and events in this world, is trueexactly if it savesthe phenomena. (ibid.)
Characterization (Observability)
X is observable if there are circumstances which are such that, if X ispresent to us under those circumstances, then we observe it. (1072)
Christian Wthrich Topic 11
S i tifi li d th i l t
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
The theory/observation dichotomy
Two questions:
1 Can we divide our language into a theoretical andnon-theoretical part? (van Fraassen, 1071)
No, because language is thoroughly theory-infected.2 [C]an we classify objects and events into observable and
unobservable ones? (ibid.)
Maxwell: no, because theres continuum of cases that liebetween direct observation and inference
van Fraassen: yes, because although observable is vaguepredicate is still useful as it has clear cases andcounter-cases
Christian Wthrich Topic 11
Scientific realism and the no miracles argument
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
Observability according to van Fraassen
Clear cases
(observable entities)
tables and chairs
moons of Jupiter
winged horses
Clear counter-cases
(unobservable entities)
elementary particles
forces
the big bang
Christian Wthrich Topic 11
Scientific realism and the no miracles argument The pessimistic meta induction
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
The pessimistic meta-induction
Underdetermination
Taking a larger view: the base rate fallacy
The pessimistic meta-induction (PMI) for antirealism
(Reconstruction courtesy of Juha Saatsi (2005))
Proponents: (Poincar), Laudan
(1) Assume that success of theory reliably indicates truth.
(2) So most current successful theories are true.(3) Then most past scientific theories are false, since theydiffer significantly from current theories.(4) Many of these past theories were also successful.
So success of a theory is not a reliable indicator of itstruth.
defuses NMA, but does not by itself establish antirealism
Christian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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Scientific realism and the no-miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
The pessimistic meta-induction
Underdetermination
Taking a larger view: the base rate fallacy
Stronger version of PMI
(Reconstruction courtesy of Juha Saatsi (2005))
(1) Most successful theories (current and past) are taken tobe false by current lights.(2) Current successful theories are not essentially different
from past successful theories with respect to theirobservable content.(3) (By argument on previous slide) success of a theory isnot a reliable indicator of its truth, and there is no otherreliable indicator of truth.
Current successful theories are probably false bystatistical reasoning.
if sound, establishes antirealism
Christian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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Scientific realism and the no miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
The pessimistic meta induction
Underdetermination
Taking a larger view: the base rate fallacy
Realist strategy in the face of strong NMI
Structural realism(Poincar, Worrall, Ladyman, French)
there exists a cumulative continuity through revolutions capturedby underlying (mathematical) structure of theories
non-cumulative aspects (stark shifts in ontology) responsible for
falsity of theories as viewed latermore than carrying over successful empirical content
less than carrying over full theoretical content
continuity of structure, not content of theories
only be realist with respect to structure of theory
claim: avoid PMI, accounts for NMA
problem: notion of structure insufficiently developed and applied
Christian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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Scientific realism and the no miracles argument
Constructive empiricism
Antirealism and the pessimistic meta-induction
The pessimistic meta induction
Underdetermination
Taking a larger view: the base rate fallacy
Underdetermination of theory by evidence argument
antirealists: there is always range of theories compatible withactual evidence, and maybe always a range of theoriescompatible with allpossibleevidence
we have never good grounds on which to choose one theoryover its empirically equivalent competitors
Challenge:
Find episode in history of science where we have truly beenconfronted with two or more empirically equivalent, but otherwiseinequivalent theories
Christian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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g
Constructive empiricism
Antirealism and the pessimistic meta-induction
p
Underdetermination
Taking a larger view: the base rate fallacy
Base rate fallacy and realist ennui
(Magnus and Callender (2004))
Suppose there is a disease with inevitable, unique, identifiablesymptoms taking some time to show.
reliable test for disease identifying people who do not yet showsymptoms
Dx: xhas disease;Px: xtests positive
assumeP(Px|Dx) =1
assume there is a small chance if someone is healthy, theynevertheless test positive (false positive), e.g.
P(Px|Dx) =0.05
now suppose patientatests positive: what is the probability thatshe actually has disease, i.e.P(Da|Pa) =?
it is tempting to argue as follows...
Christian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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g
Constructive empiricism
Antirealism and the pessimistic meta-induction
p
Underdetermination
Taking a larger view: the base rate fallacy
P(Pa) =1, P(Pa|Da) =1, P(Px|Da) =0.05 P(Da|Pa) 0
Problem: is disease is rare in population, e.g. if only 1 in 1000
people has the disease, then given the assumptions, we shouldexpect about 51 in 1000 to test positive; of these, only 1 hasdisease; thus, chance thatahas disease is 1 in 51 or roughlyP(Da|Pa) =0.02
assumption thatP(Pa) =1 not true given this population
Magnus and Callender: both NMA and PMI commit this fallacy
because we dont know the base rate (= probability that arandom theory among all present candidate theories is true), wecannot make any inference about whether success is reliableindicator for truth
just as: if we dont know the relative frequency of disease inpopulation, we dont know whether a positive test is a reliableindicator for presence of disease
because it boils down to our incompatible intuitions about base
rate, theres ennui in the realism debateChristian Wthrich Topic 11
Scientific realism and the no-miracles argument The pessimistic meta-induction
8/13/2019 Lect11 Realism
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Constructive empiricism
Antirealism and the pessimistic meta-induction
Underdetermination
Taking a larger view: the base rate fallacy
So perhaps the logical empiricists were right in claiming that
the debate is meaningless...?
Christian Wthrich Topic 11