Aristotle (384-322 BCE) is, along with Plato, one of the principal ancient Greek philosophers. Aristotle’s metaphysics is partly based on Plato’s ideas, but reflects a more pragmatic and less mystical interpretation of reality. Aristotle proposes that all things are divided into “universals” and “substances.” Substances are particular things, whereas universals are types or classes of things. Furthermore, a substance can have qualities which are inherent to it.

Substances consist of a union of form and matter: In the case of a marble statue, the matter is the marble, and the form is the shape of the statue. Aristotle believes that a human being has two parts, the soul (form) and the body (matter). The form is what makes a particular piece of matter one coherent and particular thing. Form thus constitutes the essence, or defining nature, of a thing. The relation of form to matter is that of actuality to potentiality: Bare matter is potential, and it becomes actual by acquiring a particular form.

Aristotle’s ideas about ethics are contained in three treatises, the most important of which is the Nicomachean Ethics. Russell sees the Ethics as embodying common sense and the values of “decent, well-behaved citizens” (173).