WorrallWorrall’’s Structural s Structural Realism: Realism:

The Best of Both The Best of Both Worlds?Worlds?

Kareem KhalifaKareem Khalifa

Department of PhilosophyDepartment of Philosophy

Middlebury CollegeMiddlebury College

OverviewOverview

• No Miracles, No PessimismNo Miracles, No Pessimism– Revision 1: No Miracles with No Revision 1: No Miracles with No

ExplanationsExplanations– Revision 2: Whittling Down the Hit Revision 2: Whittling Down the Hit

Parade with Novel PredictionsParade with Novel Predictions– Revision 3: The Continuity of Revision 3: The Continuity of

Theoretical ScienceTheoretical Science– Revision 4: The Continuity and Reality Revision 4: The Continuity and Reality

of Structuresof Structures

No Miracles ArgumentNo Miracles Argument

• Scientific theories are empirically Scientific theories are empirically successful.successful.

• The approximate truth of these The approximate truth of these theories best explains their theories best explains their empirical success.empirical success.

• So scientific theories are So scientific theories are approximately true.approximately true.

• The Pessimistic Induction attacks The Pessimistic Induction attacks the 2the 2ndnd premise. premise.

No Miracles, No No Miracles, No Explanations—Explanations—

No Problem! (102)No Problem! (102)• Worrall doesnWorrall doesn’’t see the No Miracles t see the No Miracles

Argument as an IBE, but rather as Argument as an IBE, but rather as asserting only that asserting only that ““a theorya theory’’s s predictive success supplies a predictive success supplies a prima prima faciefacie plausibility argument in favor plausibility argument in favor of its somehow or other having of its somehow or other having latched onto the truth.latched onto the truth.”” (102) (102)

WorrallWorrall’’s 1st Revision to s 1st Revision to the the

No Miracles ArgumentNo Miracles Argument• Scientific theories are empirically Scientific theories are empirically

successful.successful.• The approximate truth of these The approximate truth of these

theories theories best explainsbest explains their their empirical success.empirical success.

• So scientific theories are So scientific theories are approximately true.approximately true.

• The empirical success of these theories The empirical success of these theories makesmakes

it highly plausibleit highly plausible that they are approximately true. that they are approximately true.

Benefits of this RevisionBenefits of this Revision• This avoids the Petitio PrincipiiThis avoids the Petitio Principii

– No Miracles uses IBE; IBE presupposes that the No Miracles uses IBE; IBE presupposes that the best explanation is true; presupposing the best best explanation is true; presupposing the best explanation is true = realism; so No Miracles explanation is true = realism; so No Miracles presupposes realismpresupposes realism

– In contrast, Worrall makes the weaker claim that In contrast, Worrall makes the weaker claim that No Miracles uses a commonsense plausibility No Miracles uses a commonsense plausibility argument (evidence makes this more likely than argument (evidence makes this more likely than not) that doesnnot) that doesn’’t presuppose realism t presuppose realism

• It also avoids the weakness of the realist It also avoids the weakness of the realist ““explanationexplanation””– ““A requirement for a convincing A requirement for a convincing scientificscientific

explanation is explanation is independent independent testability…Yet in the testability…Yet in the case of realismcase of realism’’s s ‘‘explanationexplanation’’ of the success of our of the success of our current theories there can be … no question of any current theories there can be … no question of any independent tests.independent tests.””

– WorrallWorrall’’s No Miracle Argument doesns No Miracle Argument doesn’’t appeal to t appeal to explanations at all.explanations at all.

DrawbackDrawback

• It makes the Pessimistic Induction even It makes the Pessimistic Induction even worse!worse!

• If a theoryIf a theory’’s empirical success makes its s empirical success makes its approximate truth plausible, then there approximate truth plausible, then there should be few/no empirically successful should be few/no empirically successful but false theories.but false theories.

• But there are! Recall the Hit Parade!But there are! Recall the Hit Parade!– ……or see the next slide…or see the next slide…

• So a theorySo a theory’’s empirical success need not s empirical success need not make its approximate truth plausible.make its approximate truth plausible.

The Hit ListThe Hit List• The crystalline spheres of ancient and The crystalline spheres of ancient and

medieval astronomymedieval astronomy• The humoral theory of medicineThe humoral theory of medicine• The effluvial theory of static electricityThe effluvial theory of static electricity• ‘‘CatastrophistCatastrophist’’ geology, including Noah geology, including Noah’’s Floods Flood• The phlogiston theory of chemistryThe phlogiston theory of chemistry• The caloric theory of heatThe caloric theory of heat• The vibratory theory of heatThe vibratory theory of heat• The vital force theories of physiologyThe vital force theories of physiology• The electromagnetic aetherThe electromagnetic aether• The optical aetherThe optical aether• The theory of circular inertiaThe theory of circular inertia• Theories of spontaneous generationTheories of spontaneous generation

Whittling Down the Hit Whittling Down the Hit ListList

• Worrall thinks many members of the Worrall thinks many members of the Hit Parade are not Hit Parade are not ““genuinelygenuinely”” empirically successful:empirically successful:– ““Not every empirical consequence that Not every empirical consequence that

a theory has and which happens to be a theory has and which happens to be correct will give intuitive support for correct will give intuitive support for the idea that the theory must somehow the idea that the theory must somehow or other have latched onto the or other have latched onto the ‘‘universal blueprint.universal blueprint.’”’” (101) (101)

Predictive Novelty as Predictive Novelty as Genuine Empirical SuccessGenuine Empirical Success

• Worrall gives a more precise definition of novelty:Worrall gives a more precise definition of novelty:• EE is a novel prediction of a theory is a novel prediction of a theory TT if if TT was was

constructed:constructed:– Without knowledge of Without knowledge of E E oror– Without using Without using EE to fix an initially free parameter to fix an initially free parameter

in in TT..• A A free parameterfree parameter is a number used to define a is a number used to define a

theory thoroughly enough so as to make useful theory thoroughly enough so as to make useful predictions. This number should be determined by predictions. This number should be determined by experiment but some theories include parameters experiment but some theories include parameters that have not been verified by observation.that have not been verified by observation.

• So if So if EE is used to determine a free parameter of is used to determine a free parameter of TT, , then then E E implies implies TT, so , so T T trivially implies trivially implies EE..

Example of free Example of free parameterparameter

• Free parameter in Ptolemaic system: Free parameter in Ptolemaic system: # of epicycles# of epicycles

• This free parameter is determined This free parameter is determined by measurements of movements of by measurements of movements of planets in the night skyplanets in the night sky

• So any prediction of those So any prediction of those movements from Ptolemaic system movements from Ptolemaic system will not be novel.will not be novel.

Furthermore…Furthermore…

• EE should be an empirical should be an empirical generalizationgeneralization; ; not just a specific, one-shot instance (114)not just a specific, one-shot instance (114)

• Generalization: Generalization: WheneverWhenever the the circumstances are circumstances are CC, the outcome will be , the outcome will be X.X.– Ex. Newton: The motion of the planets arises Ex. Newton: The motion of the planets arises

from empirical generalizations about centripetal from empirical generalizations about centripetal motion.motion.

• One-shot: In this particular circumstance, One-shot: In this particular circumstance, the outcome will be the outcome will be XX..– Ex. Ptolemy: Each planet has a unique size and Ex. Ptolemy: Each planet has a unique size and

speed of epicycle.speed of epicycle.

WorrallWorrall’’s 2nd Revision to s 2nd Revision to the the

No Miracles ArgumentNo Miracles Argument• Scientific theories Scientific theories are empirically are empirically

successfulsuccessful..• The The empirical successempirical success of these of these

theories makes it highly plausible theories makes it highly plausible that they are approximately true.that they are approximately true.

• So scientific theories are So scientific theories are approximately true.approximately true.

• Scientific theories Scientific theories make general, novel make general, novel predictionspredictions..• The The general, novel predictionsgeneral, novel predictions of these of these theories theories

makes it highly plausible that they are makes it highly plausible that they are

approximately true.approximately true.

DrawbackDrawback

• The Problem of Scientific Revolutions: If our The Problem of Scientific Revolutions: If our current theories are approximately true, current theories are approximately true, then past theories that are discontinuous then past theories that are discontinuous with our current theories are false.with our current theories are false.

• There are past theories discontinuous with There are past theories discontinuous with our current ones that predicted novel our current ones that predicted novel empirical generalizations.empirical generalizations.

• So itSo it’’s not always plausible to infer from s not always plausible to infer from novel empirical generalizations to novel empirical generalizations to approximate truth. approximate truth.

Transitivity of Approximate Transitivity of Approximate TruthTruth

• Worrall: So realists must claim that past Worrall: So realists must claim that past theories are not discontinuous with our theories are not discontinuous with our current theories.current theories.– ““Realists need to claim that although some Realists need to claim that although some

presently accepted theory may subsequently presently accepted theory may subsequently be modified and replaced, it will still look be modified and replaced, it will still look ‘‘approximately trueapproximately true’’ in the light, not just of in the light, not just of the next theory which supersedes it, but the next theory which supersedes it, but also in the light of the theory which also in the light of the theory which supersedes the theory which supersedes it, supersedes the theory which supersedes it, etc.etc.”” (105) (105)

More on approximate More on approximate truthtruth

• The transitivity of approximate truth of past The transitivity of approximate truth of past theories must occur at the level of theoretical theories must occur at the level of theoretical statements about unobservables.statements about unobservables.– Antirealism is compatible with past theoriesAntirealism is compatible with past theories ’’ having having

cumulative approximate truth at the level of cumulative approximate truth at the level of observables.observables.

• In other words, theory change must be In other words, theory change must be continuous.continuous.

• As stated, this is merely a counter-assertion. As stated, this is merely a counter-assertion. The details of how theory change is continuous The details of how theory change is continuous constitute structural realism (coming soon!).constitute structural realism (coming soon!).

WorrallWorrall’’s 3rd Revision to s 3rd Revision to thethe

No Miracles ArgumentNo Miracles Argument• Past scientific theories make Past scientific theories make

general, novel predictions.general, novel predictions.• The general, novel predictions of The general, novel predictions of

these theories makes it highly these theories makes it highly plausible that they are plausible that they are approximately trueapproximately true..

• So past scientific theories are So past scientific theories are approximately true.approximately true.

• The general, novel predictions of The general, novel predictions of these theories these theories makes it highly plausible that they makes it highly plausible that they are are continuous continuous with our current theories.with our current theories.• Our current theories are Our current theories are approximately true.approximately true.

The The ““chalk and cheesechalk and cheese”” challenge for the continuity challenge for the continuity

requirementrequirement• Worrall is worried that even these Worrall is worried that even these

requirements might not take care of all of requirements might not take care of all of the episodes in the history of science.the episodes in the history of science.

• There are novelly predictive theories that There are novelly predictive theories that are discontinuous with our current are discontinuous with our current theories.theories.– Ex. FresnelEx. Fresnel’’s disk!s disk!

• Furthermore, there is an empirical Furthermore, there is an empirical continuity that is unquestionable. (108-continuity that is unquestionable. (108-109)109)

• So realism is not out of the woods yet…So realism is not out of the woods yet…

More on chalk and More on chalk and cheesecheese

• There needs to be something that is There needs to be something that is theoretical and continuous.theoretical and continuous.

• Worrall: Continuity occurs at the level Worrall: Continuity occurs at the level of of ““structure.structure.””– Structure = unobserved relations Structure = unobserved relations

between observables, typically expressed between observables, typically expressed by mathematical equations.by mathematical equations.

– Quoting Poincaré: FresnelQuoting Poincaré: Fresnel’’s s ““equations equations express relations, and if the equations express relations, and if the equations remain true, it is because the relations remain true, it is because the relations preserve their realitypreserve their reality””

What is structure?What is structure?

• A A structurestructure is defined a is defined a domaindomain of objects and of objects and a a set of relationsset of relations between those objects. between those objects.

• Ex. Let the domain be {Twilight Rm. 303, Ex. Let the domain be {Twilight Rm. 303, Kareem Khalifa} and the set of relations be Kareem Khalifa} and the set of relations be {…is the office of…}. That’s a {…is the office of…}. That’s a concreteconcrete structure.structure.

• SR deals with SR deals with abstractabstract structures, which are structures, which are purely formal (extensional) and require no purely formal (extensional) and require no interpretation (no intension) beyond the interpretation (no intension) beyond the formalism.formalism.

• Domain = {aDomain = {a11, a, a22}, Relations = {<a}, Relations = {<a11,a,a22>}>}

Back to structural Back to structural realismrealism

• Original formulation: all we can know Original formulation: all we can know about the unobservable world is its about the unobservable world is its structurestructure..

• This means: all we can know about the This means: all we can know about the unobservable world is that:unobservable world is that:1.1. It has the same It has the same numbernumber of objects as are of objects as are

posited by our theories;posited by our theories;

2.2. Its objects stand in the Its objects stand in the same set-theoretic same set-theoretic relations relations as our theory claims of its as our theory claims of its respective objects.respective objects.

Fresnel ExampleFresnel Example

• Fresnel: The unobservables are waves of ether• Maxwell: No, they’re electromagnetic fields• Both: set of equations on 119• Worrall: So we can say that the light source, the visible

light, disks, etc. really stand in the relation described by the equations.

• But we canBut we can’’t say what things make up that relation.t say what things make up that relation.

All unobservable

WorrallWorrall’’s Final revision to s Final revision to the No Miracles Argumentthe No Miracles Argument

• Past scientific theories make general, Past scientific theories make general, novel predictions.novel predictions.

• The general, novel predictions of these The general, novel predictions of these theories makes it highly plausible that theories makes it highly plausible that they they areare continuous with our current continuous with our current theories.theories.

• Our current theories Our current theories are approximately are approximately truetrue..

• So past scientific theories So past scientific theories are are approximately trueapproximately true..

• The general, novel predictions of The general, novel predictions of these theories these theories makes it highly plausible that they makes it highly plausible that they have have structures that arestructures that are continuous with continuous with our current our current theories.theories.• Our current theories Our current theories have have approximately true approximately true structuresstructures.. • So past scientific theories have have approximately approximately true structurestrue structures..