If it seems shocking to some that scientists are not cold computers but human beings with different preferences, dispositions, skills and temperament… - Julian Baggini

That is why there can be no one account that is ‘the truth’, not because ‘truth’ is beyond us. We need to distinguish between an account which is ‘the truth’ and one which is ‘truthful’. If by ‘the truth’ of a life we mean the one, true, complete account of it, then no such truths can be told. But we can tell more or less truthful stories about our lives and those of others: ones that do not gloss over embarrassing facts, ones that reveal many sides of a personality and not just those we wish to promote. Relating such a truthful story is not about cataloguing the largest possible number of true facts about a person. That is why our commitment to truth and rationality requires that our conceptual maps only include genuine features of what we are mapping and do not leave out anything that a user of that map might reasonably be expected to find useful. But the idea that we can come up with any kind of conceptual map that does not reflect our values and interests is a mirage. Philosophical autobiography helps us to see that behind all reasoning is a reasoner who can never drain away all her individuality.

In this way we can see that political reason is as much – if not more – bottom-up than top-down. Rationality requires attending to objective reasons for belief and many of the most important such reasons are provided by what we observe in the world. Indeed, what we observe is of primary importance: there is no hope of understanding justice, for example, if we attempt to do so purely by examining the concept without any reference at all to what we perceive to be just or unjust in the world.

Only our most intimate friends know our deepest flaws, and in the same way the greatest skeptics about reason should be those who seek to defend it. If we do not debunk the grandiose myths of reason then its enemies will do so far more destructively. My positive case for rationality therefore requires taking us through four key myths of rationality, all of which can be traced back to Plato. These myths are: that reason is purely objective and requires no subjective judgement; that it can and should take the role of our chief guide, the charioteer of the soul; that it can furnish us with the fundamental reasons for action; and that we can build society on perfectly rational principles.