Emile Durkheim

A monomaniac is a sick person whose mentality is perfectly healthy in all respects but one; he has a single flaw, clearly localized. At times, for example, he has an unreasonable and absurd desire to drink or steal or use abusive language; but all his other acts and all his other thoughts are strictly correct.

A person is not merely a single subject distinguished from all the others. It is especially a being to which is attributed a relative autonomy in relation to the environment with which it is most immediately in contact.