Hume's Law, according to which an ought cannot result from an is, and its reciprocal, according to which an is cannot result from an ought, occupy salient positions in discussions on metaethics. In this paper I will show logical relations between distinct formulations of Hume's Law and of its reciprocal. I will show, also, how these formulations are related to theses sustained by important thinkers such as Poincaré, Nelson, Jörgensen and Hare.
Hume's Law; reciprocal of Hume's Law; metaethics; Poincaré; Nelson; Jörgensen; Hare