Environmental ethics in its modern classical expression by Aldo Leopold appears to fall afoul of Hume’s prohibition against deriving ought-statements from is-statements since it is presented as a logical consequence of the science of ecology. Hume’s is/ought-dichotomy is reviewed in its historical theoretical context. A general formulation bridging is and ought, in Hume’s terms, meeting his own criteria for sound practical argument, is found. It is then shown that Aldo Leopold’s land ethic is expressible as a special case of this general formulation. Hence Leopold’s land ethic, despite its direct passage from descriptive scientific premises to prescriptive normative conclusions, is not in violation of any logical strictures which Hume would impose upon axiological reasoning.