Most humanists would consider themselves to be rationalists. That is to say, they are committed to something like the view that rational reflection is the best method of determining the truth and how we should live. Whatever the limits of reason, it is preferable to hunch, supposed revelation, tradition or authority.

In philosophy, however, 'rationalism' means something much more specific. Rationalists hold that the most basic truths and beliefs can be known a priori - that is to say, independently from sense experience. In contrast, empiricists maintain that only trivial truths can be established by reason alone. To know anything about the real world, we require the data of experience.

British philosophy has generally been of a more empiricist bent. In what sounds like the preamble to a bad joke, an Englishman, an Irishman and a Scotsman - Locke, Berkeley and Hume - began a tradition of British empiricism in the seventeenth and eighteenth centuries which ran counter the rationalism of the Frenchman Descartes and the Dutchmen Spinoza and Leibniz. Rationalism has been a minority pursuit in the British isles ever since.

Rationalism is not, however, a philosophical dead duck by any means. For one thing, the division between empiricism and rationalism is not as neat as many philosophy primers would have you believe. Early in the last century, Bertrand Russell made this public knowledge in his introductory work, The Problems of Philosophy, in which he claimed that the 'rules of thought' - the basic principles of logic and reasoning used by empiricists and rationalists alike - were a priori in nature. Since these rules of thought are by no means trivial, but part of the very foundations of philosophy, even the most hard-nosed empiricist, although correct in many respects, must grant something to the rationalist.

Christopher Peacocke's The Realm of Reason continues this debate and is further evidence of a recent rationalist revival in Anglo-American philosophy. The particular focus of this new work is a theory of entitlement: what entitles a thinker to form a given belief. But it is by no means confined to addressing this very specific problem. Its wider ambition is to 'make a start on articulating a general rationalist position'.

Within academic philosophy, this is no doubt a work of some importance. But is it of any interest to the more general species of rationalist, the person who may know little about the differences between Descartes and Hume but who prefers the broadly rational approach of both to the flakier alternatives?

In some ways it is, for the simple reason that the kinds of issues Peacocke discusses are exactly the same as those that interest anyone who cares about rationality and what it means.

On this view, the only thing that might make Peacocke's arguments seem irrelevant to the concerns of the rationalist on the street is that the discussion is conducted in terms which presuppose a highly specialised knowledge of a voluminous literature which non-academics cannot be supposed to have read. This doesn't make the book impenetrable, but it does mean the general reader has to work very hard at it indeed.

There is another problem. Even professional philosophers may feel that Peacocke is addressing a very localised group of thinkers. Its terms of reference are, for the most part, recent British and American philosophers of a particular stripe, more often than not natives of Oxford and the two Cambridges of Massachusetts and England.

Take for example, this sentence from the introduction: "Substantive theories of intentional content and of understanding are as essential to developing the rationalist conception as are systematic formal theories of referential semantics and truth."

What this means is that Peacocke's project requires a theoretical apparatus supplied by his peers and predecessors. But this apparatus is peculiar to what is in historical terms an extremely local and particular branch of philosophy.

If you think this branch is simply the right one, none of this is problematic. But if you suspect that in the long run, Peacocke et al are not going to contribute to the great canon that includes Plato, Hume and Wittgenstein, then the general reader need not be put off reading The Realm of Reason merely because of its difficulty. That need not imply a criticism of Peacocke's book or his style of philosophy. It may simply suggest it is just wrong to expect all philosophy to be relevant to the interests of all who value rationality, or even all philosophers.