Authors of the second generation of the analytic movement devoted to moral philosophy (most notably Hare and Nowell-Smith) consider that the problems of this discipline consist in identifying the unique notes of moral language. In this context, one of the keys of their theoretical proposals is the formulation of Hume's law, which would prevent the reduction of value judgments to factual statements, thus avoiding the confusion between practical and descriptive language. The purpose of this paper is to show how, within this formulation, certain assertions of a nominalist and empiricist epistemology appear as necessary assumptions, without which the law loses its logical sense and ability to oppose moral theories categorized by these authors as "naturalists".