- the material cause is the stuff from which the thing is made;
- the formal cause is the pattern or structure it has;
- the efficient cause is the agent that imposed this form on that matter; and
- the final cause is the purpose for the thing.
Thus, for example, the material cause of this chair is the wood out of which it is made, the formal cause is the shape into which it was fashioned, the efficient cause was the carpenter by whom the chair was made, and the final cause is the sitting for the sake of which it was designed. In the case of living beings, Aristotle supposed, the soul is the formal, efficient, and final cause; the body is only the material cause.
(Via Philosophical Dictionary)