Twinning, substance, and identity through time: a reply to McMahan

Abstract

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In "Killing Embryos for Stem Cell Research," Jeff McMahan argues against the proposition that we are essentially individual human organisms. The author shows that the term "essentially" is insufficiently defined by McMahan and, if we take the typical explication of the concept by modal metaphysicians, the claim "we are essentially human beings" is true, contrary to McMahan's argument. The author offers a counterexample to McMahan's implicit acceptance of the principle that only beings who have developed the capacity for self-consciousness are the proper subjects of moral worth.