Body, Soul, and Sense in Nature

Aristotle’s well-known definition of the soul is found in On the Soul 2.1, 412a19: the soul is the form or actualization (entelekheia) of a natural or organic body which potentially has life. In other words, the soul is the principle through which living beings are alive and have different capacities such as nutrition, reproduction, perception, desire, and thinking. Non-human animals and plants share the most basic capacities, i.e. nutrition and reproduction. Perception and desire, however, are powers that pertain to non-human and human animals. Within his biological treatises Aristotle conceived a sort of phylogenetic scale, according to which inferior non-human animals possess at least the sense of touch while higher forms of life, for instance mammals, have five external senses and more complex capacities such as common sense, memory, and imagination. Human animals share the capacities performed by plants and non-human animals, but in the particular case of humans an exclusive and unique capacity is added: thinking.