Lect11 Realism

8/13/2019 Lect11 Realism

1/15


2/15

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


3/15


4/15




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


5/15




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


S i ifi li d h i l


6/15




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)


S i tifi li d th i l t


7/15




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


Scientific realism and the no miracles argument


8/15




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


Scientific realism and the no miracles argument The pessimistic meta induction


9/15




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


Scientific realism and the no-miracles argument The pessimistic meta-induction


10/15




The pessimistic meta-induction

Underdetermination


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




11/15




The pessimistic meta induction

Underdetermination


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




12/15




The pessimistic meta induction

Underdetermination


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




13/15

g



p

Underdetermination


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...




14/15

g



p

Underdetermination


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



15/15



Underdetermination


So perhaps the logical empiricists were right in claiming that

the debate is meaningless...?


Documents

Lect11 Realism