This paper explicates and argues for the thesis that individual rational judgment, of the kind required for rational justification in non-formal, substantive domains – i.e. in empirical knowledge or in morals (both ethics and justice) – is in fundamental part socially and historically based, although these social and historical aspects of rational justification are consistent with realism about the objects of empirical knowledge and with strict objectivity about basic moral principles. The central thesis is that, to judge fully rationally that (...) one judges – in ways which provide rational justification of one’s judgment about any substantive matter – requires recognising one’s inherent fallibility and consequently also recognising our mutual interdependence for assessing our own and each others’ judgments and their justification. This explication provides a pragmatic account of rational justification in substantive domains which puts paid to the traditional distinction, still influential today, between ‘rational’ and ‘historical’ knowledge. (Note: This paper is a counterpart to Westphal 2011b; each paper contains substantial material not included in the other.). (shrink)