This paper hinges on a distinction between two principles, one political and the other moral. The political principle is that diversity in public opinion and private pursuits is acceptable, and that it is not the business of the state to impose uniformity. The moral principle is that diversity in moral judgement is inescapable, and that there are conflicts which moral philosophy cannot hope to remove. The question that I want to examine is this: to what extent, if at all, does the former principle depend upon the latter? Or, applying labels to the two principles which I hope are not misleading, to what extent, if at all, does liberalism depend upon moral pluralism? The answer that I shall argue for is that liberal political principles do not depend on pluralist moral principles at all, and that many recent interpretations of liberalism are wholly mistaken in the views which they advance regarding its moral foundations. This paper is, then, a critical one, but in the course of its argument some suggestions about what could supply liberalism with an appropriate foundation should emerge.