Aristotle's Psychology: On the Soul and Parva Naturalia

soul is concerned. Thought, growth, and decay are modes of the single life of the organism. Aristotle, therefore, conceived his entire psychology under a biological form.

Everything that moves itself contains a duality of moving principle and thing moved, i.e. a duality of ‘form’ and ‘matter,’ to use Aristotle’s metaphysical terminology. Every living thing, a plant no less than a man, is a composite being (σύνολον composite whole), viz. a composite of soul and body. The soul is the cause of motion and change, and is therefore the ‘efficient cause’; it is further that which determines the form or individuality of the organism, and is therefore the ‘formal cause’; it is also the end for which the body exists, and is, for this reason, the ‘final cause.’ The body is the ‘material cause’ or condition of the composite, while the soul represents all of the principles of activity in the organism. Soul is defined by Aristotle as the “entelechy or complete realization of a natural body endowed with the capacity of life.”1 The soul or vital principle is not itself corporeal, although it is inseparable from the body, as form is inseparable from matter.2 Soul and body are not distinct things that do or can exist apart. Their separation is only notional. They no more exist apart than do concave and convex.

Soul is to be found in every part of the body. This is observable in the case of graftings, where the entire parent form can be reproduced from a section. Insects live for some time after bisection, but they do not continue to live

1 De an. 412a 20, 412b 5.
2 This does not apply to the Prime Mover as pure ‘form.’ The relation of the active reason to the body is discussed below in the chapter on Reason (chap. viii.).