Bernard Williams, answered from the texts and cited to the page.
Truthfulness is a complex of two virtues: accuracy (the disposition to get things right, to take care that one's beliefs match how things are) and sincerity (the disposition to assert what one actually believes). These are virtues that a community of language-users needs in order to function as a community of language-users at all. The State of Nature genealogy in Truth and Truthfulness traces why these dispositions matter: a community in which speakers do not care to get things right, or assert what they do not believe, cannot sustain the practices of inquiry, deliberation, and trust that give human communities their distinctively human shape.123
The genealogy is "vindicatory" rather than "debunking": showing the origin of these dispositions in human need vindicates them as values without requiring metaphysical correspondence-truth as their foundation. Truth itself remains a regulative ideal — what accuracy aims at — but the truth in question is not the metaphysical correspondence-truth that figures in absolute conceptions of reality.
The radical contingency of the ethical thesis cuts across this: our ethical conceptions, like our conceptions of truth, might have been different, and the recognition of this contingency is part of what mature reflection delivers.45
These will be particularly important when we move beyond beliefs that straightforwardly embody pieces of information. But for now, at our entry to the State of Nature, we concentrate on the basic phenomenon of people's beliefs' contributing to there being a shared pool of information: various observers are in different T H R E E situations, and they then transport to the pool beliefs (in the favourable case, true…Truth and Truthfulness, pp. 44–45
GENEALOGY 1. Real and Fictional The subject of this book is truthfulness: various virtues and practices, and ideas that go with them, that express the concern to tell the truth—in the sense both of telling the truth to other people and, in the first place, telling the true from the false.Truth and Truthfulness, pp. 20–21
So, institutions of trust, which every society needs in some form, demand that there should be some dispositions to think that telling the truth (to the right people, on the right occasions) is in itself a good thing. What form those dispositions will take in different societies at different times is a matter of real history.Essays and Reviews 1959-2002, p. 408
They are useful, indeed essential, to such objectives as the pooling of information, and those objectives are important to almost every human purpose. In taking us so far, the story has led us some way toward the idea that truthfulness has a value. However, there is more than one way in which what the story has given us so far is limited.Truth and Truthfulness, pp. 58–59
We can also urge it against alternative creeds whose own self-understandings (as divine revelations, for instance) are themselves not going to survive a genealogical inquiry.Essays and Reviews 1959-2002, p. 411
Truth and Truthfulness (2002) is Williams's late synthesis of his work on truth, virtues, and the genealogical method. Putnam engaged the absolute-conception framework critically across decades (Reason, Truth and History 1981; Renewing Philosophy 1992; the 2001 reply to "Philosophy as a Humanistic Discipline"). The deflationary tradition (Horwich) is a different challenge: it accepts truthfulness as a virtue but denies that truth has any substantive metaphysical content, including the thin metaphysical content Williams's regulative-ideal version retains. The vindicatory-genealogy method has been taken up by Raymond Geuss and Edward Craig (Knowledge and the State of Nature, 1990) for related projects in epistemology and political theory. Blackburn's chapter in Callcut's Reading Bernard Williams (2008) is the most sustained engagement with the Putnam-Williams debate.