Rationalism, empiricism, structuralism, scepticism, existentialism, pragmatism … Philosophers like to talk of their great and dead predecessors in terms of –isms. Lecture courses, seminar series and conferences are organized under the heading of one –ism or another. But if you were to ask a contemporary philosopher in the English-speaking world – one of the living and thus not so great – to classify her philosophical position, I would wager that the most common answer would be: “I'm a naturalist”. It is certainly the answer I would give. Naturalism is the current philosophical fashion, at least in this part of the world.

What, then, is this fashionable naturalism? It is certainly true that all naturalists share an admiring attitude towards science; and like all philosophical positions naturalism has its slogans: “There is no first philosophy”; “Philosophy is continuous with the natural sciences”. But like most slogans, they tell us little. Philosophers are inclined to think that when a term is in common usage, without a clear definition, that is when they are most needed. They roll up their sleeves and set to work to find necessary and sufficient conditions for something to be X. That is not what I intend to do in this book. I doubt if there is any such definition for naturalism. Like most of the other –isms in philosophy, naturalism embraces many differing views.

To understand adequately the various things that naturalism can and might mean we shall need to look in detail at the many different naturalist philosophers and examine their points of agreement and difference.