Stanford’s Antirealist Explanation of the Success of Science

Kyle Stanford's ‘Antirealist explanation of the success of science' (Stanford 2000) does no better either. Jack Smart suggested long ago that the Copernican astron­omer can explain the predictive success of Ptolemaic astronomy by showing that it generates the same predictions as the Copernican theory does and by assuming the truth of the Copernican theory.

Consider a man (in the sixteenth century) who is a realist about the Copernican hypothesis but instrumentalist about the Ptolemaic one. He can explain the instrumental usefulness of the Ptolemaic system of epicycles because he can prove that the Ptolemaic system can produce almost the same predictions about the apparent motions of the planets as does the Copernican hypothesis. Hence the assumption of the realist truth of the Copernican hypothesis explains the instrumental usefulness of the Ptolemaic one. Such an explanation of the instrumental usefulness of certain theories would not be possible if all theories were regarded as merely instrumental. [Smart (1968), p. 151.]

Now by the ‘instrumental usefulness' of Ptolemaic astronomy, Smart obviously means its predictive success. So, his suggestion is that realists can explain the predictive success of a false theory in terms of its predictive similarity to the true theory. Stanford considers Smart's suggestion, and says of it:

Notice that the actual content of the Copernican hypothesis plays no role whatsoever in the explanation we get of the success of the Ptolemaic system: what matters is simply that there is some true theoretical account of the domain in question and that the predictions of the Ptolemaic system are sufficiently close to the predictions made by that true theoretical account. [Stanford (2000), p. 274.]

This is quite wrong. The detailed content of the Copernican theory, and the fact that some of the detail of the Ptolemaic theory is similar to it, is essential to the explanation of the success of Ptolemaic theory.

Stanford suggests that “it is the fact that the Ptolemaic system is predictively similar to the true theoretical account of the relevant domain that explains its usefulness, not that it is predictively similar to the Copernican hypothesis as such.” (ibid, 275). This, again, is quite wrong. No explanation, or no good explanation, of Ptolemy's usefulness is to be had simply by saying that it makes the same pre­dictions as the true theory does. For this is just to say “It is predictively as if Ptolemy's theory were true”.

Stanford generalises this example into an antirealist explanation of success in general. The predictive success of any theory is to be explained by saying that the theory makes the same predictions as the true theory (whatever that is). But this is explaining “T is predictively successful” by saying “It is predictively as if T were true”, or for short, “T is predictively successful”.

Stanford says, in defence of his proposal, that unlike the realist, constructive empiricist and surrealist proposals, which all appeal to some relationship between the theory and the world to explain its success, his proposal “does not appeal to a relationship between a theory and the world at all; instead it appeals to a rela­tionship of predictive similarity between two theories'” (ibid, 276). This seems to be a double joke. First, there are not two theories here at all, there is one theory and an existential claim that there is some true theory somewhere predictively similar to it. Second, you hardly explain the success of T by saying “T is predictively similar to some other theory T*”, for T* might be false and issue in false predictions. The truth of T*, whether T* is spelled out or just asserted to exist (as here), is essential to the explanation of T’s success. The relation of T* to the world is essential, in other words. [Note that Stanford’s proposal collapses into the realist proposal if we allow T* to be identical with T. For then we explain the success of T by saying that it is predictively similar to some true T*, namely T itself. Nothing in Stanford’s presentation rules this out. In particular, predictive similarity is a reflexive relation, which every theory bears to itself. However, Stanford obviously wants his proposal to be a rival to the realist proposal, so we ought in charity to assume that T and T* are distinct theories.]

Stanford counts it a virtue of his proposal that it does not involve asserting the truth of any particular theory—all that is asserted is that there is some true theory T* predictively similar to T. It might be thought that, simply by invoking the truth of some unspecified theory or other, Stanford’s proposal remains a realist proposal.

In the Ptolemy-Copernicus case, the empirical success of a false theory (Ptol­emy) is explained by invoking its similarity to a true theory (Copernicus). The similarity explains why the two theories make the same predictions—the truth of the second theory explains why the predictions of the first theory are true even though the first theory is false. The surrealist transform of Ptolemy’s theory —“Observed planetary motions are as if Ptolemy’s theory were true”—follows from Ptolemy’s theory and from Copernicus’s. Realists about Copernicus become surrealists about Ptolemy, in order to explain the empirical adequacy of Ptolemy. But Copernican realism, not Ptolemaic surrealism, is doing the explaining here. Copernicus tells us why the phenomena are as if Ptolemy were true.

The key premise of the Miracle Argument was that the truth of a theory is the best explanation of the empirical adequacy of that theory. So far, at least, that key premise seems to be correct. From which it follows, provided we accept IBE, that it is reasonable to believe that an empirically adequate theory is true. (Of course, this argument assumes a realist theory of truth, which makes of truth something more than empirical adequacy. If we go in for an ‘empirical adequacy theory of truth', which collapses truth into empirical adequacy, then the Miracle Argument also collapses.)

There are two worries about the argument so far.

It should really be obvious that explanatory virtues do not always go hand-in-hand with evidential virtues. The ancients explained the motions of the fixed stars by saying that they were fixed on the surface of an invisible celestial sphere which rotates once a day around the central earth. Compare that hypothesis with its surrealist transform, the hypothesis that the stars move as if they were fixed to such a sphere. The realist hypothesis is explanatory, the surrealist hypothesis is not, despite the fact that the latter is expressly designed to be evidentially equivalent with the former. Similarly with the nineteenth-century geological theory of fossil formation, G, and Philip Gosse's surrealist transform G*: God created the universe in 4004 BC as if G were true. There are quite different explanations here, but no geological evidence can decide between them—it was not on evidential grounds that nineteenth-century thinkers rejected G* out of hand.

These examples are meant to show that realists should not be browbeaten by the fact that antirealists can come up with alternative hypotheses to the realist ones which empirical evidence cannot exclude. These alternatives can be excluded on explanatory grounds. Either they provide no explanations at all, or only incredible ones. It is the same with antirealist explanations of the success of scientific theories in terms of their empirical adequacy (however precisely formulated). Such expla­nations are either no explanations at all, or completely inadequate circular ones, and can be rejected as such. This, if accepted, only shows that the realist explanation of science's success is better than some antirealist ones. Perhaps there is another antirealist explanation that we have not yet considered? And in any case, how good an argument for realism is it, that the truth of a theory best explains its empirical adequacy?

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