Big Questions: Philosophy of Science Handout 3 Dr. H. Beebee Scientific Realism & Anti-Realism Introduction Scientific theories claim, or at least seem to claim, that the universe is populated by a host of entities that we cannot observe in any obvious sense: we have genes, quarks, curved space-time, the superego (if you think psychoanalysis is a science) etc. etc. Do we (including scientists) have any right to believe in such entities? Scientific realists say yes - such entities really do exist - while anti-realists say no. There are three basic positions which one can adopt on this issue: Realism: We have very good reason to believe that the unobservable entities postulated by well-confirmed theories exist. “Constructive empiricism”: We have no good reason to suppose that such entities exist. The evidence which supports scientific theories supports only the claim that such theories are “empirically adequate” - that what they say about observable entities is true. We have no reason to suppose that what they say about unobservable entities is true. Instrumentalism: This is a thesis about the meaning of “theoretical” terms (i.e. terms which appear to refer to unobservable entities). Instrumentalists claim that such terms don’t really refer to any such entities. A theory employing theoretical terms is really only “about” the observable world: what makes the theory true is the observable facts being the way the theory says they are. Theoretical terms are introduced into a theory only to make it simpler or more elegant. Their presence does not indicate any ontological commitment to unobservable entities “referred” to by the terms, since the terms don’t, despite initial appearances, refer to such entities.

For example, suppose that Quantum Mechanics makes a claim about the quantum state of a particular photon. None of the realist, constructive empiricist or instrumentalist need deny that Quantum Mechanics is a hugely successful theory for predicting and explaining the outcomes of all sorts of experiments. None of them think there’s anything wrong with Quantum Mechanics. Rather, they disagree over: (a) what the theory is really telling us about the world when it says that, say, the photon is in state S, (b) whether we have any good reason to believe this, and

(c) what the purpose of a theory like Quantum Mechanics is. Realism and constructive empiricism agree on (a): the theory is telling us exactly what it appears to be telling us, namely, that the photon really is in quantum state S. But they disagree on (b): the realist thinks we have every reason to believe what the theory says about the quantum state, whereas the constructive empiricist thinks we have no reason to believe it. Does it follow that the constructive empiricist takes rather a dim view of Quantum Mechanics? After all, if the aim of science is truth (and this is what the realist thinks), and we have no reason whatever to suppose that what current science tells us about the unobservable is true, it follows that we have no reason to suppose that Quantum Mechanics is doing what a scientific theory ought to be doing, namely, telling us the truth about the universe.

1 But the constructive empiricist does not take such a dim view of Quantum Mechanics because she does not believe that the aim of science is truth. Rather, she thinks the aim of science is empirical adequacy: what we want and need from scientific theories is not the whole truth, but merely the truth about observable phenomena. It doesn’t matter very much what a theory says about the unobservable, so long as it gets its predictions right. So we shouldn’t really be concerned that we’ve got no reason to believe what Quantum Mechanics says about the photon’s quantum state - so long as the observable consequences of this claim are borne out. Instrumentalism, on the other hand, disagrees with both realism and constructive empiricism over (a). According to instrumentalism, what Quantum Mechanics is really saying when it says that the photon is in quantum state S is merely that, if I were to make such-and-such a measurement, I would get so-and-so observable results. The terms “photon” and “quantum state” are not intended to refer to real features of the world; rather they have a purely instrumental role. “The photon is in state S” is just a more convenient and more elegant way of saying “doing this experiment would get you these results”. Both forms of anti-realism (instrumentalism and constructive empiricism)thus agree, against the realist, that the primary aim of science is to get to the truth about the observable world - that is, empirical adequacy.

Two arguments for scientific realism 1. The “no-miracles” (or “Ultimate”) argument Many realists regard this argument as the strongest motivation for scientific realism: It would be a miracle, a coincidence on a near cosmic scale, if a theory made as many correct empirical predictions as, say, the general theory of relativity or the photon theory of light without what that theory says about the fundamental structure of the universe being correct or “essentially” or “basically” correct. But we shouldn’t accept miracles, not at any rate if there is a non-miraculous alternative. If what these theories say is going on “behind” the phenomena is indeed true or “approximately true” then it is no wonder that they get the phenomena right. So it is plausible to conclude that presently accepted theories are indeed “essentially” correct. (Worrall, p.101) Put simply: It would be a miracle if the universe behaved by and large - as it does - as if there were quarks and fields and photons, if in fact there were no such things. But we shouldn’t believe in miracles. The best explanation of why scientific theories are so successful - of why the universe behaves as if there were quarks and fields and photons - is that there really are such entities. Hence we ought to believe that realism is true.

An anti-realist response The no-miracles argument basically says that the only sensible explanation of the predictive success of scientific theories is that what those theories say about the unobservable entities which give rise to the predicted phenomena is true. But Bas van Fraassen, the inventor of constructive empiricism, has another explanation ...... science is a biological phenomenon, an activity by one kind of organism which facilitates its interaction with the environment. And this makes me think that a very different kind of scientific explanation is required.

2 I can best make the point by contrasting two accounts of the mouse who runs from its enemy, the cat. St. Augustine ... provided an intentional explanation: the mouse perceives that the cat is its enemy, hence the mouse runs. What is postulated here is the ‘adequacy’ of the mouse’s thought to the order of nature: the relation of enmity is correctly reflected in his mind. But the Darwinist says: Do not ask why the mouse runs from its enemy. Species which did not cope with their natural enemies no longer exist. That is why there are only ones who do. In just the same way, I claim that the success of current scientific theories is no miracle ... For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive - the ones which in fact latched on to actual [observable] regularities in nature. (The Scientific Image, pp. 39-40)

2. Argument from causal explanation Often we explain why a particular phenomenon occurred by saying what caused it; and often the entities which play a part in the causal explanation of a phenomenon are unobservable ones. But it seems that in such cases the explanation only counts as a genuine explanation if the alleged cause really exists. ... when I explain the change in rate in fall of a light droplet in an electric field, by asserting that there are positrons or electrons on the ball, I am inferring from effect to cause, and the explanation has no sense at all without the direct implication that there are electrons or positrons on the ball. (Nancy Cartwright, How the Laws of Physics Lie, p.92)

An anti-realist response Van Fraassen denies that we need to attribute a causal role to unobservable entities in order that our purported causal explanations make sense. Rather, he thinks, ‘talk of underlying causal mechanisms can be construed as talk about the internal structure of ... models’ (p.80). The idea here is that, for the purposes of explanation, we (or rather, scientists) “immerse” themselves in their theories; and, when so immersed, speak as though the picture of unobservable reality which those theories provide is accurate. Thus they speak as if there are unobservable entities with causal powers. But when they do this, what they’re really doing is simply saying something about how their theory or “model” fits together - and not saying anything about how (unobservable) reality fits together.

The observable/unobservable distinction One way of trying to undermine the anti-realist’s position is to concentrate on the alleged distinction between what is and what is not observable. The constructive empiricist is committed to the view that there is such a distinction; but this is debatable. Van Fraassen, for example, thinks that when you look into a cloud chamber, what you observe is a vapour trail; you (wrongly, in his view) infer from this observation that there’s a particle there that’s causing the vapour trail. Whereas when you look at normal medium-sized objects like tables, you just straightforwardly observe the table itself. But one could claim that the cloud chamber and table cases aren’t really very different. For when I look at a table, what I really “observe” is a certain surface appearance: a brown 4-sided shape, say. I infer from this observation that there really is a 3-dimensional solid table present; but, just as in the cloud chamber case, I do not

3 directly observe the table. So there isn’t really a distinction between observable and unobservable entities. Hence there’s no good reason to believe in “observable” entities but to suspend belief in “unobservable” entities: sub-atomic particles, magnetic fields and so on are no less observable than are chairs, tables and people. Another strategy against the constructive empiricist is to argue that even if there is an observable/unobservable distinction, we ought not to be completely sceptical about unobservable entities merely on the grounds that we can’t actually see them. For any observable entity which we have never actually observed, we can have good or bad evidence that it exists. Why should we not likewise have good or bad evidence that an unobservable entity exists? Alan Musgrave puts the point like this: On any plausible theory of evidential support one would have to admit that there could be far better evidence for an explanation couched in terms of unobservables than for an explanation couched in terms of observables. Is the evidence for the existence of electrons better or worse than the evidence for the existence of the yeti or of the mouse in van Fraassen’s wainscoting? It is a curious sort of empiricism which sets aside the weight of available evidence on the ground that a casual observer might one day see his mouse or yeti, while the scientist can never see (but only detect) his electrons. (in Churchland and Hooker, p.206)

Reading B. van Fraassen: The Scientific Image (Q175.V335), chs. 1 & 2 N. Cartwright How the Laws of Physics Lie (QC6.C3586), chs. 4 & 5 A. O’Hear An Introduction to the Philosophy of Science, chs. 5 & 6 P. Churchland & C. Hooker (eds.): Images of Science (Q175.I46) I. Hacking Representing and Intervening (Q175.H2), chs. 1 & 16 S. Psillos ‘On van Fraassen’s critique of abductive reasoning’, Philosophical Quarterly 46 (Jan.1996) (B1.P455) R. Boyd ‘Realism, underdetermination and a causal theory of evidence’, Nous 7 (1973) (B1.N6) G. Maxwell ‘The ontological status of theoretical entities’, Minnesota Studies in Philosophy of Science III (1962) (Q175.M64) J. Worrall ‘Structural Realism: The Best of Both Worlds’, Dialectica 1989 (B1.D48)

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