Aristotle distinguished four kinds of causes: material, formal, efficient, and final. The Greek word, aition, which is often translated as “cause,” actually means, “the being of a thing.” Thus, for Aristotle there are as many senses of causation as there are senses of “being” to be explained. The four were: the material cause, the formal cause, the efficient cause, and the final cause.
A thing’s material cause is the matter that constitutes the thing. Think of bits of clay arranged in a certain way so as to constitute, say, a Giacometti statue. The clay so arranged is the material cause of the statue. In terms of “being,” the material being of the statue is the constituent bits of clay arranged statue-wise. The question a material causal explanation answers is, What is the thing constituted by?
The formal cause of a thing—or the formal being of a thing—is the thing’s essence. What makes the thing be the thing it is? Even though we no longer really think in terms of essences of things, we still kind of get it. Aristotle’s example: the formal cause or essence of the human being was that it was a rational animal. Being a rational animal is the definition of what makes a human being a human being, and is what keeps a chimpanzee from being a human being.
A thing’s efficient cause is a precipitating, antecedent event often mechanistically related to the thing coming to have some property or other. Efficient causation is more familiar to us. The rock she threw broke the window. The hurricane caused the building to collapse.
Aristotle’s “final” cause is the telos, or end, or purpose of a thing, as said above.
Aristotle’s “final” cause is the telos, or end, or purpose of a thing, as said above.
Digression: Does the word “television” have the same root as the word “teleology”? Yes. But what could those two things have in common? We’ve got to remember that the ancient Greeks were producing new ideas, ideas they did not yet have words for. When they wanted to talk abstractly or philosophically about the purpose of a thing, the word they used came from an existing word meaning “end,” like the end of a long walk. What’s the purpose of a long walk? To get to where you are going, to get to the end. The abstract notion of an end or a goal or purpose came from the simpler idea of “far away” which is what telos meant before the Greeks started philosophizing about essential purposes and essential goals of things. It is that meaning—“far away’—that gives us the “tele” in television. (And if you can dig it, notice that when we went to name the new fangled device allowing moving images and audio to be broadcast into living rooms across America, we called it essentially “far away vision” or “seeing stuff that’s far away,” i.e., television.) End of digression.
Final causes are teleological explanations, which, again, are explanations of a thing by reference to its purpose. To take a famous example: the oak, for Aristotle, is the final cause of the acorn, the far away goal of the acorn. (This means the future-oak is the cause of the present-acorn. You can see why Renaissance scientists, whose aim was to find and describe patterns of efficient cause and effect in nature, would not like final causation: it has the cause coming later in time than the effect!)
Asking for a final cause of an acorn is like asking, What is the purpose of this acorn? Its purpose is the oak it will become. But the acorn also has a material cause, a formal cause and an efficient cause. In other words, the acorn has constituents that make it up, it has an essence, and it has a causal history. Organic matter is the material cause of the acorn. The formal cause is what it is to be an acorn, its definition or essence, what keeps it from being a pine cone, say. And the efficient cause is the tree that grew the acorn and then dropped it into our inquisitive hands.