Certain restrictions on public funding for assisted reproductive technology (ART) are articulated and defended by recourse to a distinction between medical infertility and social infertility. We propose that underlying the prioritization of medical infertility is a vision of medicine whose proper role is to restore but not to improve upon nature. We go on to mark moral responses that speak of investments many continue to make in nature as properly an object of reverence and gratitude and therein (sometimes) a source of moral guidance. We draw on the work of Ludwig Wittgenstein in arguing for the plausibility of an appeal to nature in opposition to the charge that it must contain a logical fallacy. We also invite consideration of the moral plausibility of some appeal to nature. Finally, we examine what follows in the case of ART. Should medicine respect as natural limits that should not be overcome: the need for a man and a woman in reproduction; menopause; and even declining fertility with age? We must first ask ourselves to what degree we should defer to nature in the conduct of medicine, at least in the particular if not the general case. This will involve also asking ourselves what we think is natural and in what instances and spirit might we defy nature. Divergent opinions and policies concerning who should receive ART treatment and public funding are more easily understood in view of the centrality, complexity and fundamental nature of these questions.