What is the ergon of human beings, asks Thomas Nagel in his essay on Aristotle’s eudaimonia, for the answer to the question of how to live hangs on this. The ergon (function) of the hammer is to pound in nails; a poor hammer may be too heavy to wield, too flimsy, too poor at pound in nails, etc.; a good hammer may even be called perfect if it pounds in nails most excellently. But what of the ergon of human beings?
As Nagel reads Aristotle, the function of humans cannot be what we share in common with plants or animals (or angels). Locomotion, for instance, we share in common with animals, but analyzing human beings in terms of locomotion would not help us to understand in what eudaimonia (human flourishing) might consist. Survival and reproduction are other erga, but these too we share with animals. In neither case do we have the distinct ergon without which it remains vague what will make human living matter. (To see the force of this point, imagine providing food and shelter for your children. You can do so and, as a parent, it would be the right thing to do, but yet what would be the point of raising children well?)