As regards material substance, we must not fail to realize that even if all things are derived from the same primary cause, or from the same things as primary causes¹; i.e. even if all things that are generated have the same matter for their first principle, nevertheless each thing has some matter peculiar to it; e.g., “the sweet” or “the viscous” is the proximate matter of mucus, and “the bitter” or some such thing is that of bile— although probably mucus and bile are derived from the same ultimate matter. The result is that there is more than one matter of the same thing, when one thing is the matter of the other; e.g., mucus is derived from “the viscous”; and from “the sweet,” if “the viscous” is derived from “the sweet”; and from bile, by the analysis of bile into its ultimate matter. For there are two senses in which X comes from Y; either because X will be found further on than Y in the process of development, or because X is produced when Y is analyzed into its original constituents. And different things can be generated by the moving cause when the matter is one and the same, e.g. a chest and a bed from wood. But some different things must necessarily have different matter; e.g., a saw cannot be generated from wood, nor does this lie in the power of the moving cause, for it cannot make a saw of wool or wood. If, then, it is possible to make the same thing from different matter, clearly the art, i.e. the moving principle, is the same; for if both the matter and the mover are different, so too is the product. So whenever we inquire what the cause is, since there are causes in several senses, we must state all the possible causes. E.g., what is the material cause of a man? The menses. What is the moving cause? The semen. What is the formal cause? The essence. What is the final cause? The end. 1044b(But perhaps both the latter are the same.) We must, however, state the most proximate causes. What is the matter? Not fire or earth, but the matter proper to man. Thus as regards generable natural substances we must proceed in this manner, if we are to proceed correctly; that is, if the causes are these and of this number, and it is necessary to know the causes. But in the case of substances which though natural are eternal the principle is different. For presumably some of them have no matter; or no matter of this kind, but only such as is spatially mobile.² Moreover, things which exist by nature but are not substances have no matter; their substrate is their substance. E.g., what is the cause of an eclipse; what is its matter? It has none; it is the moon which is affected. What is the moving cause which destroys the light? The earth. There is probably no final cause. The formal cause is the formula; but this is obscure unless it includes the efficient cause. E.g., what is an eclipse? A privation of light; and if we add “caused by the earth’s intervention,” this is the definition which includes the 〈efficient〉 cause. In the case of sleep it is not clear what it is that is proximately affected. Is it the animal? Yes; but in respect of what, and of what proximately? The heart, or some other part. Again, by what is it affected? Again, what is the affection which affects that part, and not the whole animal? A particular kind of immobility? Yes; but in virtue of what affection of the proximate subject is it this?

Since some things both are and are not, without being liable to generation and destruction³—e.g. points,⁴ if they exist at all; and in general the forms and shapes of things (because white does not come to be, but the wood becomes white, since everything which comes into being comes from something and becomes something)—not all the contraries⁵ can be generated from each other. White is not generated from black in the same way as a white man is generated from a black man; nor does everything contain matter, but only such things as admit of generation and transformation into each other. And such things as, without undergoing a process of change, both are and are not, have no matter. There is a difficulty in the question how the matter of the individual is related to the contraries. E.g., if the body is potentially healthy, and the contrary of health is disease, is the body potentially both healthy and diseased? And is water potentially wine and vinegar? Probably in the one case it is the matter in respect of the positive state and form, and in the other case in respect of privation and degeneration which is contrary to its proper nature. There is also a difficulty as to why wine is not the matter of vinegar, nor potentially vinegar (though vinegar comes from it), and why the living man is not potentially dead. In point of fact they are not; their degeneration is accidental, 1045aand the actual matter of the living body becomes by degeneration the potentiality and matter of the dead body, and water the matter of vinegar; for the one becomes the other just as day becomes night. All things which change reciprocally in this way must return into the matter; e.g., if a living thing is generated from a dead one, it must first become the matter, and then a living thing; and vinegar must first become water, and then wine.

With regard to the difficulty which we have described⁶ in connection with definitions and numbers, what is the cause of the unification? In all things which have a plurality of parts, and which are not a total aggregate but a whole of some sort distinct from the parts, there is some cause ; inasmuch as even in bodies sometimes contact is the cause of their unity, and sometimes viscosity or some other such quality. But a definition is one account, not by connection, like the Iliad, but because it is a definition of one thing. What is it, then, that makes “man” one thing, and why does it make him one thing and not many, e.g. “animal” and “two-footed,” especially if, as some say, there is an Idea of “animal” and an Idea of “two-footed”? Why are not these Ideas “man,” and why should not man exist by participation, not in any “man,” but in two Ideas, those of “animal” and “two-footed”? And in general “man” will be not one, but two things—“animal” and “two-footed.” Evidently if we proceed in this way, as it is usual to define and explain, it will be impossible to answer and solve the difficulty. But if, as we maintain, man is part matter and part form—the matter being potentially, and the form actually man—, the point which we are investigating will no longer seem to be a difficulty. For this difficulty is just the same as we should have if the definition of X⁷ were “round bronze”; for this name would give a clue to the formula, so that the question becomes “what is the cause of the unification of “round” and “bronze”?” The difficulty is no longer apparent, because the one is matter and the other form. What then is it (apart from the active cause) which causes that which exists potentially to exist actually in things which admit of generation? There is no other cause of the potential sphere’s being an actual sphere; this was the essence of each.⁸ Some matter is intelligible and some sensible, and part of the formula is always matter and part actuality; e.g., the circle is a plane figure.⁹ But such thing¹⁰ as have no matter, neither intelligible nor sensible, are ipso facto each one of them essentially something one; 1045bjust as they are essentially something existent: an individual substance, a quality, or a quantity. Hence neither “existent” nor “one” is present in their definitions. And their essence is ipso facto something one, just as it is something existent. Hence also there is no other cause of the unity of any of these things, or of their existence; for each one of them is one and “existent” not because it is contained in the genus “being” or “unity,” nor because these genera exist separately apart from their particulars, but ipso facto. It is because of this difficulty that some thinkers¹¹ speak of “participation,” and raise the question of what is the cause of participation, and what participation means; and others speak of “communion”; e.g., Lycophron¹² says that knowledge is a communion of the soul with “knowing”; and others call life a combination or connection of soul with body. The same argument, however, applies in every case; for “being healthy” will be the “communion” or “connection” or “combination” of soul and health; and “being a bronze triangle” a “combination” of bronze and triangle; and “being white” a “combination” of surface and whiteness. The reason for this is that people look for a unifying formula, and a difference, between potentiality and actuality. But, as we have said,¹³ the proximate matter and the shape are one and the same; the one existing potentially, and the other actually. Therefore to ask the cause of their unity is like asking the cause of unity in general; for each individual thing is one, and the potential and the actual are in a sense one. Thus there is no cause other than whatever initiates the development from potentiality to actuality. And such things as have no matter are all, without qualification, essential unities.