The position I have defended is that any choice of a conceptual scheme presupposes values, and the choice of a scheme for describing ordinary interpersonal relations and social facts, not to mention thinking about one's own life plan, involves, among other things, one's moral values. One cannot choose a scheme which simply 'copies' the facts, because no conceptual scheme is a mere 'copy' of the world. The notion of truth itself depends for its content on our standards of rational acceptability, and these in turn rest on and presuppose our values. Put schematically and too briefly, I am saying that theory of truth presupposes theory of rationality which in turn presupposes our theory of the good.
‘Theory of the good', however, is not only programmatic, but is itself dependent upon assumptions about human nature, about society, about the universe (including theological and metaphysical assumptions). We have had to revise our theory of the good (such as it is) again and again as our knowledge has increased and our world-view has changed.
It has become clear that in the conception I am defending there is no such thing as a 'foundation'. And at this point people become worried: are we not close to the view that there is no difference between 'justified' and 'justified by our lights' (relativism) or even 'justified by my lights' (a species of solipsism)?
The position of the solipsist is indeed the one we will land in if we try to stand outside the conceptual system to which the concept of rationality belongs and simultaneously pretend to offer a more 'rational' notion of rationality! (Many thinkers have fallen into Nietzsche's error of telling us they had a 'better' morality than the entire tradition; in each case they only produced a monstrosity, for all they could do was arbitrarily wrench certain values out of their context while ignoring others.) We can only hope to produce a more rational conception of rationality or a better conception of morality if we operate from within our tradition (with its echoes of the Greek agora, of Newton, and so on, in the case of rationality, and with its echoes of scripture, of the philosophers, of the democratic revolutions, and so on, in the case of morality); but this is not at all to say that all is entirely reasonable and well with the conceptions we now have. We are not trapped in individual solipsistic hells, but invited to engage in a truly human dialogue; one which combines collectivity with individual responsibility.
– Hilary Putnam in Reason, Truth, and History (1981)