Formal cause

The "four causes" are elements of an influential principle in Aristotelian thought whereby explanations of change or movement are classified into four fundamental types of answer to the question "why?". 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 where identifying a "cause" is difficult, or in which "causes" might merge, Aristotle was convinced that his four "causes" provided an analytical scheme of general applicability.

Aitia, from Greek αἰτία was the word that Aristotle used to refer to the causal explanation that has traditionally been translated as "cause", but this specialized, technical, philosophical usage of the word "cause" does not correspond to its most usual uses in everyday language. The translation of Aristotle's αἰτία that is nearest to current ordinary language is "explanation". In this article, the peculiar philosophical usage of the word "cause" will be employed, for tradition's sake, but the reader should not be misled by confusing this technical usage with current ordinary language.

Aristotle held that there were four kinds of answers to "why" questions (in Physics II, 3, and Metaphysics V, 2):

The four "causes" are not mutually exclusive. For Aristotle, several 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, a complete explanation, taking into account the four aitias, 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 such because a carpenter made it starting from a tree (agent), it has these dimensions because it is to be used by men and women (end).

In his philosophical writings, Aristotle used the Greek word , aition, a neuter, singular form of an adjective. The Greek word had meant, perhaps originally in a "legal" context, what or who is 'responsible', mostly but not always in a bad sense of 'guilt' or 'blame'; alternatively it could mean 'to the credit of' someone or something. The appropriation of this word by Aristotle and other philosophers reflects how the Greek experience of legal practice influenced the concern in Greek thought to determine what is responsible. The word developed other meanings, including its use in philosophy in a more abstract sense. About a century before Aristotle, the anonymous author of the Hippocratic text On Ancient Medicine had described the essential characteristics of a cause: "We must, therefore, consider the causes (αίτια) of each [medical] condition to be those things which are such that, when they are present, the condition necessarily occurs, but when they change to another combination, it ceases." In the present context, Aristotle used the four causes to provide different answers to the question, "because of what?" The four answers to this question illuminate different aspects of how a thing comes into being or an event takes place.

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