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.

When I think about discussions at the Society for Philosophy and Psychology, a group which includes not only philosophers and psychologists, but also computer scientists and linguists, it is noteworthy that one can't always tell just from the content of particular contributions from the audience, whether a given questioner is a philosopher or an empirical scientist.

Work on causal theories of knowledge - early work by Armstrong, and Dretske, and Goldman - seemed far more satisfying. As I started to see the ways in which work in the cognitive sciences could inform our understanding of central epistemological issues, my whole idea of what the philosophical enterprise is all about began to change. Quine certainly played a role here, as did Putnam's (pre-1975) work in philosophy of science, and the exciting developments that went on in that time in philosophy of mind.

Externalists reject any such view. I think that the idea that we can tell, simply by way of reflection, whether our beliefs are justified, is deeply commonsensical. More than that, the idea that responsible epistemic agents ought to reflect on their beliefs, and hold them only if they somehow pass muster, is utterly natural.

I don't know whether I can say that having a career in philosophy has turned out as I imagined, since in many ways I had little idea of what such a life would be like. But philosophy is still tremendously exciting to me, and the opportunity to think, and talk, and write about these issues has been wonderful.

The fact that we have been able to develop a successful science, which issues in ever more accurate predictions and broader explanations, is the real ground for confidence that we are in a position to gain knowledge of the world around us. At the same time, one might ask how it is that the cognitive equipment we have came about, and here, no doubt, our evolutionary origins are relevant.

I believe, that empirically informed approaches to the question have issued in more illuminating answers than the old armchair approaches. But I think that it would be a terrible mistake to give up on addressing normative questions in epistemology.