Four causes

The four causes or four explanations are, in Aristotelian thought, categories of questions that explain "the why's" of something that exists or changes in nature. The four causes are the: material cause, the formal cause, the efficient cause, and the final cause. Aristotle wrote that "we do not have knowledge of a thing until we have grasped its why, that is to say, its cause." While there are cases in which classifying a "cause" is difficult, or in which "causes" might merge, Aristotle held that his four "causes" provided an analytical scheme of general applicability.

Aristotle's word aitia (αἰτία) has, in philosophical scholarly tradition, been translated as 'cause'. This peculiar, specialized, technical, usage of the word 'cause' is not that of everyday English language. Rather, the translation of Aristotle's αἰτία that is nearest to current ordinary language is "explanation."

In Physics II.3, I.7-9 and Metaphysics V.2, Aristotle holds that there are four kinds of answers to "why" questions:

Matter

The material cause of a change or movement. Aristotle defines matter as, "...the primary substratum of each thing, from which it comes to be per se, [substantially], and that persists in the result." - Physics I.9. Matter is what allows a thing to change, either accidentally, such as a change in shape, or substantially, such as the death of a living thing, or a compound returning to its elemental parts. Aristotle gives the examples of a table's matter being wood, or a statue's matter being bronze or marble.

Form

The formal cause of a change or movement. Aristotle defines form as, "...the terminus of the process of [change]." - Metaphysics V.4. It is what something changes into, i.e. what makes a thing what it is. Form is often confused with the whole substance, whereas it is a thing's essential difference, for example, man is a rational animal, what makes man a man, is his rationality, i.e. what makes him different from other animals.

Efficient, or Agent

The efficient or moving cause of a change or movement. This consists of things apart from the thing being changed or moved, which interact so as to be an agency of the change or movement. For example, the efficient cause of a table is a carpenter, or a person working as one, and according to Aristotle the efficient cause of a child is a parent.

Final Cause, or End

The final cause of a change or movement. This is a change or movement for the sake of a thing to be what it is. For a seed, it might be an adult plant; for a sailboat, it might be sailing; for a ball at the top of a ramp, it might be coming to rest at the bottom. Often the final cause is confused with a purpose, or intention, but this is not the case, since a purpose is the effect wanted for a thing by a person, whereas Aristotle thought of ends as always present, ungiven, and always good.

The four "causes" are not mutually exclusive. For Aristotle, several, preferably four, answers to the question "why" have to be given to explain a phenomenon and especially the actual configuration of an object. For example, if asking why a table is such and such, an explanation in terms of the four causes would sound like this: This table is solid and brown because it is made of wood (matter); it does not collapse because it has four legs of equal length (form); it is as it is because a carpenter made it, starting from a tree (agent); it has these dimensions because it is to be used by humans (end).

Aristotle distinguished between intrinsic and extrinsic causes. Matter and form are intrinsic causes because they deal directly with the object, whereas efficient and finality causes are said to be extrinsic because they are external.

Thomas Aquinas demonstrated that only those four types of causes can exist and no others. He also introduced a priority order according to which "matter is made perfect by the form, form is made perfect by the agent, and agent is made perfect by the finality." Hence, the finality is the cause of causes or, equivalently, the queen of causes.