"For Plato, the soul was something that entered the body and left it at the moment of death. For the pre-Socratics, it was a kind of spectre. Aristotle, as many know, defines the soul as the form, or the first act of the body. We need to reflect on the concept of form; form is not a part of the organism, which has its own unity. Organisms are bodies capable of performing certain functions; these capacities are obviously reduced in plants, while in animals they are already more complex. In human beings, we find activities that we call superior, such as thinking and willing. The soul is the possession of these capacities."