Chapter 3 — The four causes

From this it is plain, therefore, that there are three principles of nature: matter, form and privation. But these are not sufficient for generation. What is in potency cannot reduce itself to act: for example, the bronze which is in potency to being a statue cannot cause itself to be a statue. Rather, it needs an agent so that the form of the statue can pass from potency to act. Neither can the form draw itself from potency to act. I mean the form of the thing generated which we say is the term of generation, because the form exists only in that which has been made to be. However, what is made is in the state of becoming as long as the thing is coming to be. Therefore, it is necessary that besides the matter and form there be some principle which acts. This is called the efficient, moving, or agent cause, or that from which the principle of motion is.

Also, because, as Aristotle says in the second book of the Metaphysics, everything which acts, acts only by intending something, there must be some fourth thing: namely, that which is intended by the agent; and this is called the end. Again, we should notice that, although every agent, both natural and voluntary, intends an end, still it does not follow that every agent knows the end or deliberates about the end. To know the end is necessary in those whose actions are not determined, but which may act for opposed ends (as, for example, voluntary agents). Therefore, it is necessary that these know the end by which they determine their actions. But in natural agents the actions are determined; hence, it is not necessary to choose those things which are for the end.

Avicenna gives the following example. A harpist does not have to deliberate about the notes in any particular chord, since these are already determined for him; otherwise, there would be a delay between the notes, which would cause discord. However, it seems more reasonable to attribute deliberation to a voluntary agent than to a natural agent: and thus it is clear, by reasoning from the greater thing to the lesser, that a natural agent can intend the end without deliberation. Therefore, it is possible for the natural agent to intend the end without deliberation; and to intend this is nothing else than to have a natural inclination to something.

From the above it is plain that there are four causes: material, efficient, formal and final. But, although principle and cause are used convertibly, as is said in the fifth book of the Metaphysics, still, in the Physics, Aristotle gives four causes and three principles, because he takes as causes both what is extrinsic and what is intrinsic. Matter and form are said to be intrinsic to the thing because they are parts constituting the thing; the efficient and final causes are said to be extrinsic because they are outside the thing. But he takes as principles only the intrinsic causes. Privation, however, is not listed among the causes because it is an accidental principle, as was said. When we say that there are four causes we mean the essential causes, to which all the accidental causes are reduced, because everything which is accidental is reduced to that which is essential.

And, although Aristotle calls intrinsic causes ‘principles’ in the first book of the Physics, still, principle is applied properly to extrinsic causes, as is said in the eleventh book of the Metaphysics. ‘Element’ is used for those causes which are parts of the thing (namely, for the intrinsic causes). ‘Cause’ is applied to both. Nevertheless, one is sometimes used for the other: every cause can be called a principle and every principle a cause. However, cause seems to add something to principle as commonly used, because that which is primary, whether the existence of a posterior follows from it or not, can be called a principle: for example, the smith is called the principle of the knife because the existence of the knife comes from his operation. But when something is moved from whiteness to blackness, whiteness is said to be the principle of that motion; and universally, everything from which motion begins is called a principle. However, whiteness is not that from which the existence of blackness follows. But cause is said primarily only of that from which the existence of the posterior follows. Hence we say that a cause is that from whose existence another follows. Therefore, that primarily from which motion begins cannot really be called a cause, even though it may be called a principle. Because of this, privation is placed among the principles and not among the causes, because privation is that from which generation begins. But it can also be called an accidental cause insofar as it is coincident with matter, as was said above.

Element, on the other hand, is applied properly only to the causes of which the thing is composed, which are properly the materials. Moreover, it is not said of just any material cause, but of that one of which a thing is primarily composed; for example, we do not say that the members of the body are the elements of man, because the members also are composed of other things. Rather, we say that earth and water are the elements, because these are not composed of other bodies, but natural bodies are primarily composed of them. Hence Aristotle says, in the fifth book of the Metaphysics, that an element is that of which a thing is primarily composed, which is in that thing, and which is not divided by a form.

The explanation of the first part of the definition, that of which a thing is primarily composed, is plain from the preceding. The second part, which is in that thing, differentiates it from that matter which is entirely corrupted by generation; for example, bread is the matter of blood, but blood is generated only by the corruption of bread. Thus bread does not remain in blood; and therefore bread cannot be called an element of blood. But the elements must remain in some way, since they are not entirely corrupted, as is said in the book On Generation. The third part, and which is not divided by a form, differentiates an element from those things which have parts diverse in form (that is, in species), as the hand whose parts are flesh and bone, which differ according to species. An element is not divided into parts diverse according to species: rather, it is like water whose every part is water. For an element to exist, it need not be undivided by quantity; rather, it is sufficient that it be undivided by form. Even if it is in no way divided, it is called an element, just as letters are the elements of words. This it is plain from what was said that ‘principle,’ in some way, applies to more than does ‘cause,’ and ‘cause’ to more than does ‘element.’ This is what the Commentator says in the fifth book of the Metaphysics.