Meditations on the First Philosophy

by René Descartes

Now, when I consider the intended purpose of the clock, I could say that, since it does not indicate the time correctly, it is deviating from its own nature, and, in the same way, when I think of the machine of the human body as something formed for the motions which usually take place in it, I might believe that it, too, is deviating from its own nature, if its throat is dry when a drink does not benefit its own preservation. However, I am fully aware that this second meaning of the word nature is very different from the first. For it is merely a term that depends on my own thought, a designation with which I compare a sick person and a badly constructed clock with the idea of a healthy person and a properly constructed clock, and thus, the term is extrinsic to these objects. But by that [other use of the term nature] I understand something that is really found in things and that therefore contains a certain measure of the truth.