Anti-realism: The argument from Underdetermination

1. Anti-realism: The argument from Underdetermination “[The] point about atoms and the like is that they are purely theoretical. For all we know there could be quite different things causing what we see” (Ladyman, 160)

2. Anti-realism • To understand ‘anti-realism’, we need to contrast it with scientific realism. What is scientific realism? • Argument for anti-realism: underdetermination • What is underdetermination? • Different arguments from underdetermination • Some realist responses

3. What is scientific realism? • Scientific realism is committed to taking what scientific statements say literally • For scientific realists, what is the status of the observable/unobservable distinction? • Theoretical terms refer to unobservable entities, and statements involving them are assertoric

4. Requirements of scientific realism (158) Metaphysical requirement: Entities or kinds of entities talked about S exist Existence of entities is independent of our knowledge and minds Semantic requirement: Statements about S are irreducible and are genuinely assertoric Truth conditions for statements of S are objective and determine the truth or falsity of those statements depending on how things are in the world.

5. Requirements of scientific realism • Epistemic requirement: • Truths about S are knowable and we do in fact know some of them, hence the terms of S successfully refer to things in the world • If you were a realist about the leprechaun subatomic theory, then what would you be committed to? • Leprechauns exist mind-independently • Statements about leprechauns are about subatomic particles • These statements are true/false depending on the way the world is • Truths about leprechauns are knowable.

6. Why ‘anti-realism’? • The argument from underdetermination: • What is ‘underdetermination’? • “data underdetermine the correct theory when the data are insufficient to determine which of several theories is true” (162). • That is, more than one explanation is compatible with the evidence

7. Underdetermination • Examples: curve-fitting; Ptolemaic vs. Copernican astronomy • How to decide in cases of underdetermination? • Context and interest of investigator. Decision making sometimes involve contextual (or extra-logical) considerations

8. Underdetermination • In cases of underdetermination, would the settled on theory or explanation be necessarily the correct answer? • Suppose the theory employs theoretical terms, do those terms literally refer to unobservable entities? • What is the implication of underdetermination for scientific realism?

9. Weak form of underdetermination • “All the data we have gathered are consistent with more than one theory, we ought to suspend judgment as to which theory is true” (Ladyman 165) • For any theory T there is always another theory T* such that • 1) T & T* are weakly empirically equivalent (=both are compatible with the data gathered so far) • 2) If T & T* are weakly empirically equivalent, then there is no way to believe T and not T* • Therefore, there is no reason to believe T and not T*

10. Realist response: • The above argument is valid, but is it sound? • Does the mere existence of a rival theory consistent with the data gathered so far mean there is no reason to believe T rather than T*? • E.g. If T is highly corroborated (=predictive success), and T* is introduced ad hoc in the sense that T* can accommodate all the evidence but does not generate any new predictions itself, then which should we believe T or T*?

11. Realist response: • The weak form of the underdetermination argument is similar to the problem of induction: Every observation thus far is consistent with the claim that the next observation will be very different • The response to the weak form of underdetermination suggests that one way to answer the problem of induction is to say that the mere fact that everything observed so far is consistent with things being other wise does not mean we have no reason to believe that things will be very different the next time.

12. Duhem-Quine problem and underdetermination • Recall the Duhem-Quine problem: • 1) If (Theory + Background Assumption), then Prediction • 2) ~ Prediction • Therefore, ~ (Theory + Background Assumption) • ~ Theory or ~ Background Assumption (or both) • How do we decide which to reject?

13. Duhem-Quine problem and underdetermination • Duhem’s solution: scientist’s ‘good sense’ will pinpoint the source of the problem (170) • Duhem does not elaborate on the principles upon which ‘good sense’ rests. The idea is that the ‘evolving practice of science’ solves the problem of underdetermination • Quine holds, in practice, we rely on pragmatic considerations to solve the problem. We would consider other possibilities before changing the laws of logic. It would be impractical to abandon the laws of logic.

14. Strong form of underdetermination • How do we tell that we are not dreaming at this moment? • Some dream states are so vivid that during the dream you cannot distinguish it from wakeful states • We think we know p • If we know p then we must know that q is false • We can’t know that q is false • Therefore, we don’t know p. • That is, there is in principle no way for us to decide between p and q

15. Strong form of underdetermination • The dream hypothesis illustrates the stronger form of the underdetermination argument: The strong form says that T and T* have the “same empirical consequences, not just for what we have observed so far, but also for any possible observations we could make” (174). Consider the following: • Everything that happens is a result of random physical forces • Everything that happens is designed by God • Everything that happens is an effect of a prior cause

16. Strong form of underdetermination (174) • For every theory there exist an infinite number of strongly empirically equivalent but incompatible rival theories • If two theories are strongly empirically equivalent then they are evidentially equivalent • No evidence can ever support a unique theory more than its strongly empirically equivalent rivals • Therefore, theory-choice is radically underdetermnined.

17. Realist responses: • The first premise of the argument in the previous slide is incoherent • The first premise is false • Empirical equivalence does not imply evidential equivalence • We’ll consider the realist responses to the first premise of the argument today.

18. The first premise is incoherent • Empirical equivalence requires it to be possible to point clearly to the observable consequences of a theory. However there is no non-arbitrary distinction between observables and unobservables • The main point of this challenge: there is a continuum between clear cut cases of observables (a tree) and unobservables (a quark) • So what would count as an instance of empirical equivalence?

19. Anti-realist rejoinder: • Accept the claim that the term ‘observable’ is vague. • ‘Vague’ means a concept has borderline cases that neither clearly do nor clearly do not fall under the concept. • However, vague concepts are perfectly usable and can be used in making real distinctions • Consider ‘bald’. It is a vague concept. Yet it can be used to make distinctions. So vague concepts can do epistemological work.

20. Second objection to the first premise of the strong form of underdetermination • Second attempt: “the observable/non-observable distinction changes with time” (176). So whether or not two theories are empirically equivalent will change with time • The anti-realist will not be bothered by this challenge because the gist is that the distinction is relative with respect to time. But this just means that at any given time, theory choice would still be underdetermined

21. How about this realist response? • Are there real examples of theories that are strongly empirically equivalent? • If they were to exist, then there should be constant debates or disagreements between scientists. But this is not what we find historically. • How would the anti-realist respond? • This just shows that theory choice have been made. The question is, are there principled ways of distinguishing multiple explanations of the data?

22. Other responses to the strong form of underdetermination • We will look at the other responses to the strong form of underdetermination on Thursday