Actuality and potentiality are an important pair of concepts in Aristotle’s philosophy. Actuality means a mode of being in which a thing can bring other things about. (The Greek word translated as “actuality” literally means “putting into use” or “employment.”) Potentiality means the capacity of a thing to change or transition into different states—a state of being passive or receptive. A thing in a state of actuality can bring a thing in the state of potentiality into a state of actuality.

The examples Aristotle discusses in On the Soul involve the processes of sense perception and thought, in which a potential capacity within the human soul is actualized by the thing perceived or thought of. Indeed, Aristotle considers the soul itself to be the “first actuality of a natural body” (157)—that which brings the body to life. By extension, all form is the actualization of the potentiality of matter.

A word rich in meanings in Aristotle’s philosophy, logos can be translated in several ways. In its broadest sense it means “reason” in general. It can also mean the reason or principle behind a thing, that which makes it what it is. By extension, it can mean the verbal “account” or explanation that we give of this.