Worrall ’ s Structural Realism: The Best of Both Worlds?

1. Worrall’s Structural Realism: The Best of Both Worlds? Kareem Khalifa Department of Philosophy Middlebury College

2. Overview • No Miracles, No Pessimism • Revision 1: No Miracles with No Explanations • Revision 2: Whittling Down the Hit Parade with Novel Predictions • Revision 3: The Continuity of Theoretical Science • Revision 4: The Continuity and Reality of Structures

3. No Miracles Argument • Scientific theories are empirically successful. • The approximate truth of these theories best explains their empirical success. • So scientific theories are approximately true. • The Pessimistic Induction attacks the 2nd premise.

4. No Miracles, No Explanations—No Problem! (102) • Worrall doesn’t see the No Miracles Argument as an IBE, but rather as asserting only that “a theory’s predictive success supplies a prima facie plausibility argument in favor of its somehow or other having latched onto the truth.” (102)

5. Worrall’s 1st Revision to the No Miracles Argument • Scientific theories are empirically successful. • The approximate truth of these theories best explains their empirical success. • So scientific theories are approximately true. • The empirical success of these theories makes • it highly plausible that they are approximately true.

6. Benefits of this Revision • This avoids the Petitio Principii • No Miracles uses IBE; IBE presupposes that the best explanation is true; presupposing the best explanation is true = realism; so No Miracles presupposes realism • In contrast, Worrall makes the weaker claim that No Miracles uses a commonsense plausibility argument (evidence makes this more likely than not) that doesn’t presuppose realism • It also avoids the weakness of the realist “explanation” • “A requirement for a convincing scientific explanation is independent testability…Yet in the case of realism’s ‘explanation’ of the success of our current theories there can be … no question of any independent tests.” • Worrall’s No Miracle Argument doesn’t appeal to explanations at all.

7. Drawback • It makes the Pessimistic Induction even worse! • If a theory’s empirical success makes its approximate truth plausible, then there should be few/no empirically successful but false theories. • But there are! Recall the Hit Parade! • …or see the next slide… • So a theory’s empirical success need not make its approximate truth plausible.

8. The Hit List • The crystalline spheres of ancient and medieval astronomy • The humoral theory of medicine • The effluvial theory of static electricity • ‘Catastrophist’ geology, including Noah’s Flood • The phlogiston theory of chemistry • The caloric theory of heat • The vibratory theory of heat • The vital force theories of physiology • The electromagnetic aether • The optical aether • The theory of circular inertia • Theories of spontaneous generation

9. Whittling Down the Hit List • Worrall thinks many members of the Hit Parade are not “genuinely” empirically successful: • “Not every empirical consequence that a theory has and which happens to be correct will give intuitive support for the idea that the theory must somehow or other have latched onto the ‘universal blueprint.’” (101)

10. Predictive Novelty as Genuine Empirical Success • Worrall gives a more precise definition of novelty: • E is a novel prediction of a theory T if T was constructed: • Without knowledge of E or • Without using E to fix an initially free parameter in T. • A free parameter is a number used to define a theory thoroughly enough so as to make useful predictions. This number should be determined by experiment but some theories include parameters that have not been verified by observation. • So if E is used to determine a free parameter of T, then E implies T, so T trivially implies E.

11. Example of free parameter • Free parameter in Ptolemaic system: # of epicycles • This free parameter is determined by measurements of movements of planets in the night sky • So any prediction of those movements from Ptolemaic system will not be novel.

12. Furthermore… • E should be an empirical generalization; not just a specific, one-shot instance (114) • Generalization: Whenever the circumstances are C, the outcome will be X. • Ex. Newton: The motion of the planets arises from empirical generalizations about centripetal motion. • One-shot: In this particular circumstance, the outcome will be X. • Ex. Ptolemy: Each planet has a unique size and speed of epicycle.

13. Worrall’s 2nd Revision to the No Miracles Argument • Scientific theories are empirically successful. • The empirical success of these theories makes it highly plausible that they are approximately true. • So scientific theories are approximately true. • Scientific theories make general, novel • predictions. • The general, novel predictionsof these theories • makes it highly plausible that they are • approximately true.

14. Drawback • The Problem of Scientific Revolutions: If our current theories are approximately true, then past theories that are discontinuous with our current theories are false. • There are past theories discontinuous with our current ones that predicted novel empirical generalizations. • So it’s not always plausible to infer from novel empirical generalizations to approximate truth.

15. Transitivity of Approximate Truth • Worrall: So realists must claim that past theories are not discontinuous with our current theories. • “Realists need to claim that although some presently accepted theory may subsequently be modified and replaced, it will still look ‘approximately true’ in the light, not just of the next theory which supersedes it, but also in the light of the theory which supersedes the theory which supersedes it, etc.” (105)

16. More on approximate truth • The transitivity of approximate truth of past theories must occur at the level of theoretical statements about unobservables. • Antirealism is compatible with past theories’ having cumulative approximate truth at the level of observables. • In other words, theory change must be continuous. • As stated, this is merely a counter-assertion. The details of how theory change is continuous constitute structural realism (coming soon!).

17. Worrall’s 3rd Revision to theNo Miracles Argument • Past scientific theories make general, novel predictions. • The general, novel predictions of these theories makes it highly plausible that they are approximately true. • So past scientific theories are approximately true. • The general, novel predictions of these theories • makes it highly plausible that they are continuous • with our current theories. • Our current theories are approximately true.

18. The “chalk and cheese” challenge for the continuity requirement • Worrall is worried that even these requirements might not take care of all of the episodes in the history of science. • There are novelly predictive theories that are discontinuous with our current theories. • Ex. Fresnel’s disk! • Furthermore, there is an empirical continuity that is unquestionable. (108-109) • So realism is not out of the woods yet…

19. More on chalk and cheese • There needs to be something that is theoretical and continuous. • Worrall: Continuity occurs at the level of “structure.” • Structure = unobserved relations between observables, typically expressed by mathematical equations. • Quoting Poincaré: Fresnel’s “equations express relations, and if the equations remain true, it is because the relations preserve their reality”

20. What is structure? A structure is defined a domain of objects and a set of relations between those objects. Ex. Let the domain be {Twilight Rm. 303, Kareem Khalifa} and the set of relations be {…is the office of…}. That’s a concrete structure. SR deals with abstractstructures, which are purely formal (extensional) and require no interpretation (no intension) beyond the formalism. Domain = {a1, a2}, Relations = {<a1,a2>}

21. Back to structural realism • Original formulation: all we can know about the unobservable world is its structure. • This means: all we can know about the unobservable world is that: • It has the same number of objects as are posited by our theories; • Its objects stand in the same set-theoretic relations as our theory claims of its respective objects.

22. Fresnel Example All unobservable • 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 can’t say what things make up that relation.

23. Worrall’s Final revision to the No Miracles Argument • Past scientific theories make general, novel predictions. • The general, novel predictions of these theories makes it highly plausible that they are continuous with our current theories. • Our current theories are approximately true. • So past scientific theories are approximately true. • The general, novel predictions of these theories • makes it highly plausible that they have • structures that are continuous with our current • theories. • Our current theories have approximately true • structures. • So past scientific theories have approximately • true structures.