"If what we regard as real depends on our theory, how can we make reality the basis of our philosophy? I would say that I am a realist in the sense that I think there is a universe out there waiting to be investigated and understood. I regard the solipsist position that everything is the creation of our imagination as a waste of time. No one acts on that basis. But we cannot distinguish what is real about the universe without a theory. I therefore take the view, which has been described as simple-minded or naive, that a theory of physics is just a mathematical model that we use to describe the results of observations. A theory is a good theory if it is an elegant model, if it describes a wide class of observations, and if it predicts the results of new observations. Beyond that, it makes no sense to ask if it corresponds to reality, because we do not know what reality is independent of a theory. This view of scientific theories may make me an instrumentalist or a positivist --- as I have said above, I have been called both. The person who called me a positivist went on to add that everyone knew that positivism was out of date --- another case of refutation by denigration. It may indeed be out of date in that it was yesterday's intellectual fad, but the positivist position I have outlined seems the only possible one for someone who is seeking new laws, and new ways, to describe the universe. It is no good appealing to reality because we don't have a model-independent concept of reality."