John Gray claims that ‘value pluralism’, or the plurality and incommensurability of basic values, undermines any attempt to make a reasoned case for the superiority of liberalism (or any other ideology) over its rivals. Incommensurable values, he says, cannot be subjected to a rational ranking, except in particular cases, yet liberalism appears to advocate the promotion of certain values rather than others in general terms. I argue that Gray's critique has force against some traditional justifications of liberal politics, but that he exaggerates its reach against other, more recent forms of liberal theory. In particular, Gray's view of liberalism as merely one form of life among others, with no rational claims to precedence, rests on a mistaken understanding of the implications of value pluralism. The incommensurability of values does not imply the absolute incommensurability of forms of life, such as those of liberal and non-liberal cultures. Far from being incompatible with the reasoned advocacy of liberalism, value pluralism may itself provide liberalism with a rational grounding.