Philosophical autobiographies do much more than simply reveal the personalities and prejudices of their authors, however. They provide striking examp… - Julian Baggini

Our obsession with our differences has created the impression that there is no common domain of rationality within which disagreements can be thrashed out. We just have a multiplicity of discourses and rationalisations to legitimise different interest groups. This is not just a criticism of those currents of thought broadly and loosely labelled postmodern. The enemies of postmodernism have set themselves up as the sole champions of reason – something made easier by their opponents’ willingness to relinquish the labels of rationality and reason. In so doing they too have contributed to the sense in which the intellectual sphere is too fragmented and divided along factional lines for any general dialogue to be possible. By dismissing large sections of the intellectual community as anti-rational, the anti-postmodernists have also contributed to the sense that it is pointless to seek to argue one’s case in the widest possible forum.

This point is critical. Reason is often assumed to be by definition disinterested. Disinterested reason has its place, of course, in mathematics and science, but sometimes it can legitimately be very interested indeed. Reason needs to be objective, not disinterested, and this means it can recognise the objective existence of needs and desires, good and bad states.

This point is, in essence, the most important and overlooked one regarding the rationality of ethics. The traditional dispute between Kantians and sentimentalists rests on an assumption that to be rational, morality must be grounded on a priori principles of disinterested reason. This is false. If we understand what rationality means in an appropriately catholic way, we see that it it is a matter of providing reasons for belief and that the sources of these reasons are not confined to a priori principles of logical or scientific facts. Once we accept that, we can see that although the Kantian project of founding ethics on pure reason is doomed, reason is still at the very heart of morality.