Frankfurt

It is my view that one essential difference between persons and other creatures is to be found in the structure of a person's will. Human beings are not alone in having desires and motives, or in making choices. They share these things with the members of certain other species, some of whom even appear to engage in deliberation and to make decisions based upon prior thought. It seems to be peculiarly characteristic of humans, however, that they are able to form what I shall call "second-order desires" or "desires of the second order".