Novelty and Why Some Success Is not Surprising

I am not saying that partial success can always be explained by partial truth in this way, nor am I saying that it need be so explained. There is a kind of partial predictive success that needs no explanation at all, because it is no ‘miracle' at all— it is not even mildly surprising! Here is a simple schematic example to illustrate what I mean.

P = aQ + b, for some a and b.

When Q is 0, P is 3 (so that b = 3).

When Q is 1, P is 10 (so that a = 7).

Therefore P = 7Q + 3.

Now, the point to notice is that the hypothesis P = 7Q + 3 successfully predicts, or ‘postdicts', or at least entails that when Q is 0, P is 3, and that when Q is 1, P is 10. Are these successes miraculous, or even mildly surprising? Of course not. Those facts were used to construct the hypothesis (they were premises in the deductive argument that led to the hypothesis). It is no surprise or miracle that the hypothesis gets these things right—they were used to get the hypothesis in the first place. This trivial example illustrates a general point. Success in predicting, or post-dicting, or entailing facts used to construct a theory is no surprise. It is only novel predictive success that is surprising, where an observed fact is novel for a theory when it was not used to construct it.

Finally, a realist can say that accidents happen, some of them lucky accidents, in science as well as in everyday life.

Nancy Cartwright argues that the predictive success of science is always a kind of lucky accident. It always arises from what Bishop Berkeley called the ‘com­pensation of errors'. According to Cartwright, the laws or theories in science are always false (I shall come back to this). But scientists busy themselves to find other premises which, when combined with these false laws, will generate true predic­tions. And, scientists being clever folk, it is no wonder that they succeed. A trivial example may make the point clear. Suppose the ‘phenomenological law' we want is “Humans are two-legged', and the false law of nature we have to work with is “Dogs are two-legged”. What do we have to add to the false law to get the phe­nomenological law? Well, the auxiliary hypothesis “Humans are dogs” will do the trick. And two wrongs, carefully adjusted to each other, make a right.

Bishop Berkeley complained that the mathematicians of his day were only able to get correct results in their calculations because they systematically made mis­takes that cancelled one another out. Berkeley observed that there was nothing so scandalous as this in the reasoning of theologians. Cartwright thinks the scandal is endemic in the reasoning of physicists: “Adjustments are made where literal cor­rectness does not matter very much in order to get the correct effects where we want them; and very often... one distortion is put right by another” (Cartwright 1983, p. 140).

Now in a case like this, one would be crazy to suppose that the best explanation of the theory's predictive success is its truth.

Why does Cartwright think that the laws of physics lie, that is, are always false? The laws lie, she thinks, because they idealize or simplify things—they are false because they do not tell the whole truth. This is a mistake. “Nancy Cartwright is clever” is not false, just because it does not tell the whole truth about Nancy Cartwright. Similarly, Newton's law of gravity is not false just because it does not tell the whole truth about the forces of nature.

Never mind this. The important point is that predictive success is no miracle if the predicted facts are used to construct the theory in the first place. What is miraculous is novel predictive success. And the best explanation of such ‘miracles' is truth, either truth of wholes or truth of parts.