De principiis naturae

From what has been said, then, it is clear that there are three principles of nature, namely matter, form, and privation; these are not sufficient for generation. For what is in potency cannot reduce itself to act, just as bronze, which is potentially a statue, does not make itself into a statue, but needs a worker to draw the form of the statue from potency into act. Nor would the form draw itself from potency into act — and I speak of the form of the thing generated, which we said is the terminus of generation; for form exists only in the finished product, while what operates is in becoming, that is, while the thing is coming to be. Therefore besides matter and form there must be some principle that acts, and this is said to be the efficient cause, or mover, or agent, or that from which is the principle of motion. And because, as Aristotle says in II Metaphysics, everything that acts acts only by intending something, there must be a fourth thing, namely what is intended by the worker: and this is called the end. And it should be known that every agent, both natural and voluntary, intends an end, yet it does not follow that every agent knows the end or deliberates about the end. For to know the end is necessary in those whose actions are not determinate but are open to opposites, as voluntary agents are; and therefore they must know the end by which they determine their actions. But in natural agents the actions are determinate: hence it is not necessary to choose the means to the end. And Avicenna gives the example of the lyre-player, who need not deliberate about each plucking of the strings, since the pluckings are determinate in him; otherwise there would be a pause between pluckings, which would be discordant. But deliberation seems more characteristic of one who acts voluntarily than of a natural agent. And so it is clear by an argument from the greater that a natural agent can intend an end without deliberation: and this intending was nothing other than having a natural inclination to something. From what has been said, therefore, it is clear that there are four causes, namely the material, efficient, formal, and final. Although principle and cause are said convertibly, as is said in V Metaphysics, Aristotle nevertheless in the book of the Physics posits four causes and three principles. He takes causes for both extrinsic and intrinsic: matter and form are called intrinsic to the thing because they are parts constituting the thing; the efficient and the final are called extrinsic because they are outside the thing; but by principles he understands only intrinsic causes. Privation, however, is not named among the causes, because it is a principle per accidens, as has been said. And when we say four causes, we understand causes per se, to which however causes per accidens are reduced, because everything that is per accidens is reduced to what is per se.

But although in I Physics Aristotle posits principles for intrinsic causes, nevertheless, as is said in XI Metaphysics, principle is properly said of extrinsic causes, element of the causes that are parts of the thing, that is, of intrinsic causes, and cause is said of both; yet sometimes one is put for the other: for every cause can be called a principle and every principle a cause. Still, cause seems to add something beyond principle commonly so called, because what is first, whether the being of the later follows or not, can be called a principle, as the smith is called the principle of the knife in that the being of the knife comes from his operation; but when something is moved from blackness to whiteness, black is said to be the principle of that motion, and universally everything from which the being of motion begins is called a principle: yet blackness is not that from which the being of whiteness follows. But only that first from which follows the being of the later is called a cause: hence it is said that a cause is that from whose being another follows; and therefore the first from which the being of motion begins cannot be called a per se cause, even if it is called a principle. And for this reason privation is placed among principles and not among causes, because privation is that from which generation begins; but it can also be called a per accidens cause, insofar as it coincides with matter, as explained above.

Element, however, is properly said only of the causes from which there is composition of the thing, which are properly material; and again not of just any material cause, but of that from which the first composition comes, just as limbs are not elements of man, because limbs too are composed of other things: but we say that earth and water are elements, because these are not composed of other bodies, but from them comes the first composition of natural bodies. Hence Aristotle says in V Metaphysics that an element is that from which a thing is first composed, and is in it, and is not divided according to form.

The exposition of the first clause, from which a thing is first composed, is clear from what we have said. The second clause, namely and is in it, is added to distinguish that matter which is wholly corrupted through generation, as bread is the matter of blood, but blood is not generated unless the bread is corrupted, so bread does not remain in the blood: hence bread cannot be called an element of blood; but elements must in some way remain, since they are not corrupted, as is said in the book On Generation. The third clause, namely and is not divided according to form, is added to distinguish those things that have parts diverse in form, that is in species, as a hand whose parts are flesh and bones which differ in species; but an element is not divided into parts diverse in species, as water, every part of which is water. For it is not required for the being of an element that it not be divided according to quantity, but it suffices if it is not divided according to species; and even if it is not divided, it is called an element, as letters are called the elements of words. It is clear, therefore, that principle in a way extends more broadly than cause, and cause than element: and this is what the Commentator says in V Metaphysics.