Chemists in earlier centuries were quite interested in the nature of acids. They had no interest in analysing their concept of acid. After all, they knew that their understanding of acids was at a fairly primitive level, and what they wanted to do was understand something about the world better - the nature of acidity - not something about their own concepts.

But there is no doubt that my own views on this are, in quite a number of ways, very different from those of Quine.

I was often asked how one could even make sense of this. Isn't the category of knowledge something that we project upon the world, rather than something that we discover in it?

When we recognise that reflective processes are no more outside the causal net than unreflective processes, and that they are bound by similar constraints, we may come to understand the nature of reflection for the first time.

Rather, although belief may be adequate for explaining the behavior of individual animals - an animal which believes that p will behave no differently from an animal which knows that p - talk of knowledge is necessary once one begins to look at explaining the cognitive capacities of a species.

17th century philosophers were not in a position to understand the mind as well as we can today, since the advent of experimental methods in psychology. It shows no disrespect for the brilliance of Descartes or Kant to acknowledge that the psychology which they worked with was primitive by comparison with what is available today in the cognitive sciences, any more than it shows disrespect for the brilliance of Aristotle to acknowledge that the physics he worked with does not compare with that of Newton or Einstein.

No one would suggest that we can adequately investigate what makes something an acid, or what makes something aluminum, by bringing our pretheoretical intuitions about these things into reflective equilibrium by way of armchair theorising.