Aristotle is often thought of as one of the fathers of essentialism in Western philosophy. Aristotle’s argument for the essence of human beings is, however, much more flexible than this prejudice might suggest. In the passage about the “human function” at Nichomachean Ethics 1.7, Aristotle gives an account of the particular “function” (or “achievement,” ergon) of human beings that does not ask very much of the modern reader—only that she be prepared to analyze human beings as a logical category according to certain rules. While this may trouble the naturalistic reductionist or the post-humanist thinker, it is not clear that Aristotle’s request is unreasonable, especially given what the function argument goes on to offer. It places normative thinking in the constellation of type-property-activity, a narrowing of the search for the human good, but not an overly constrictive one. The second, substantive stage of the argument gives a more narrow interpretation of what the unique property and its corresponding activity are in the case of humans—but even here Aristotle’s apparently “thick” conclusions about the ultimate human good ultimately leave more room for a pluralistic disagreement about ends than might be expected.