Reading Aristotle: Physics 1.9: Conclusion on the Principles

This is the final chapter in Book One of Aristotle’s Physics. In the previous chapter, Aristotle responded to the view of some earlier philosophers that change (generation and corruption) is impossible by making a distinction between what Aquinas would call “essential change” and “accidental change”. He begins this last chapter:

“Others, indeed, have apprehended the nature in question, but not adequately. In the first place they allow that a thing may come to be without qualification from not-being, accepting on this point the statement of Parmenides. Secondly, they think that if the substratum is one numerically, it must have also only a single potentiality–which is a very different thing” (Physics 1.9, 191b35-192a2) [1].

In chapter eight, Aristotle concluded that those philosophers who denied “coming to be and passing away and change generally” are mistaken because they did not grasp “this nature” of essential and accidental change. Here he seems to be saying that some other philosophers “apprehended” this nature, but “not adequately”. In particular, as Aquinas points out, these philosophers “touched upon” matter, or the potency of a thing. He comments:

“Some philosophers touched upon matter, but did not understand it sufficiently. For they did not distinguish between matter and privation. Hence, they attributed to matter what belongs to privation. And because privation, considered in itself, is non-being, they said that matter, considered in itself, is non-being. And so just as a thing comes to be simply and per se from matter, so they believed that a thing comes to be simply and per se from non-being. And they were led to hold this position for two reasons. First they were influenced by the argument of Parmenides, who said that whatever is other than being is non-being. Since, then, matter is other than being, because it is not being in act, they said that it is non-being simply. Secondly, it seemed to them that that which is one in number or subject is also one in nature [ratio]. And Aristotle calls this a state of being one in potency, because things which are one in nature [ratio] are such that each has the same power. But things which are one in subject but not one in nature [ratio] do not have the same potency or power, as is clear in the white and the musical. But subject and privation are one in number, as for example, the bronze and the unshaped. Hence it seemed to them that they would be the same in nature [ratio] or in power. Hence this position accepts the unity of potency” (Lectio 15.130) [2].

Recall that per se (essential) change is change that results directly from something, while per accidens (accidental) change is change which results indirectly. Aristotle argues that something can come from “nothing” in the latter sense, where “nothing” refers to some privation. So (to continue his example from the previous chapter), if a horse somehow turns into a dog, the horse, as a horse, contains the privation “non-dog”, since, as a horse, it is currently not a dog. When it becomes a dog, the form of dog becomes from the previous form of non-dog, which is a privation and hence a “non-being”. But this is only change in an accidental sense. In an essential sense, the a change does not result from privation but from potency, the potential for that change to take place; and this potency is related to the matter of a thing. But these other philosophers, Aquinas points out, did not distinguish between matter and privation; so for them the two were equivalent. And since privation by definition is a kind of non-being, they were led to believe that matter is also a kind of non-being. But a change results per se from matter, and so they concluded that when something comes to be, it must have come to be from non-being or nothing. Why did the conflate matter and privation? Because of Parmenides’s dictum, which we’ve examined before, that everything outside of or other than being is by definition non-being. This is why Parmenides denied the possibility of any real change. If we say that, for instance, an acorn has the potency to become a tree, the “oak tree” does not actually, presently exist. It exists potentially in the acorn, but not actually. This potency is the “matter” of the acorn. But since the oak tree does not have actual being, and thus is “other than” actual being, these philosophers conclude that it, matter/potency, is non-being. This forces one to conclude either that change is impossible (as Parmenides did), or that change is possible but that something can come from nothing (which the philosophers under present consideration apparently did). The second reason for which they failed to distinguish matter and privation is that “they think that if the substratum is one numerically, it must have also only a single potentiality”. This, Aquinas tells us, they thought because “it seemed to them that that which is one in number or subject is also one in nature”. Something that is “one in nature” will have the same “power” or potency, by definition. Two acorns, for example, possessing the same nature (that of an acorn) will have the same potency: to grow and become a tree. Precisely insofar as two things have different potencies, they have different natures. But the mistake of these philosophers is in thinking that something that is one numerically, or one in subject, is necessarily one in nature. For example, a single human can be both musical and tall. The human is one individual subject, and so one numerically, but contains different “natures”, namely the nature of being tall and the nature of being musical. One subject can contain a multiplicity of natures, at least in the sense being used here. Since subject and privation are one numerically (the privation exists in the subject), these philosophers concluded that they must be one in nature and hence one in power, and so would have “only a single potentiality”. This both Aristotle and Aquinas rejects. Indeed, Aquinas gives this extra note:

“But lest anyone, because of these words, be in doubt about what the potency of matter is and whether it is one or many, it must be pointed out that act and potency divide every genus of beings, as is clear in Metaphysics, IX:1, and in Book III [L3] of this work. Hence, just as the potency for quality is not something outside the genus of quality, so the potency for substantial being is not outside the genus of substance. Therefore, the potency of matter is not some property added to its essence. Rather, matter in its very substance is potency for substantial being. Moreover, the potency of matter is one in subject with respect to many forms. But in its nature [ratio] there are many potencies according to its relation to different forms. Hence in Book Ills it will be said that to be able to be healed and to be able to be ill differ according to nature [ratio]” (Lectio 15.131) [3].

So Aristotle begins his response to the view of these philosophers:

“Now we distinguish matter and privation, and hold that one of these, namely the matter, is not-being only in virtue of an attribute which it has, while the privation in its own nature is not-being; and that the matter is nearly, in a sense is, substance, while the privation in no sense is. They, on the other hand, identify their Great and Small alike with not-being, and that whether they are taken together as one or separately. Their triad is therefore of quite a different kind than ours. For they got so far as to see that there must be some underlying nature, but they make it one–for even if one philosopher makes a dyad of it, which he calls Great and Small, the effect is the same, for he overlooked the other nature. For the one which persists is a joint cause, with the form, of what comes to be–a mother, as it were. But the negative part of the contrariety may often seem, if you concentrate your attention on it as an evil agent, not to exist at all” (192a2-16) [4].

So he makes clear that he most definitely distinguishes matter and privation. Aquinas comments:

“There is a great difference between a thing’s being one in number or subject and its being one in potency or nature [ratio]. For we say, as is clear from the above [L12 #104], that matter and privation although one in subject, are other in nature [ratio]. And this is clear for two reasons. First, matter is non-being accidentally, whereas privation is non-being per se. For ‘unshaped’ signifies non-being, but ‘bronze’ does not signify non-being except insofar as ‘unshaped’ happens to be in it. Secondly, matter is ‘near to the thing’ and exists in some respect, because it is in potency to the thing and is in some respect the substance of the thing, since it enters into the constitution of the substance. But this cannot be said of privation” (Lection 15.132) [5].

Aristotle puts it as “matter is not-being only in virtue of an attribute which it has, while the privation in its own nature is not-being”. For Aristotle, potency, while not actually existing, is not simply non-being. It is real in some sense, for otherwise it could not account for change taking place. But it is at least non-being in virtue of that which it is the potential for. For an acorn to have the potential of being a tree just means that it currently is not a tree. But this “not-ness” if you will is the entirety of privation, and so privation by nature is not-being. I think Aquinas’s example of a statue is helpful conceptually here. Imagine an artist sitting down in front of a huge mass of bronze, ready to shape it into a beautiful sculpture. At the moment, the bronze mass is “unshaped” with respect to the statue which the artist plans to form. The mass of bronze thus contains an absence or lack of the shape of the statue. The shape of the statue is, currently, non-existent. But the bronze itself, by virtue of what it is, even as an unshaped mass contains the potential to be formed into the shape of that statue. The potential of the bronze is real, and is in the bronze, even if that which it is the potential for is currently not. This is why Aristotle claims that the matter “is nearly” substance, since it is “in potency to the thing”. But a privation, insofar as it is a privation, is in potency to nothing, and has no real being, and so in in no sense a substance in itself.

When Aristotle next says “They, on the other hand, identify their Great and Small alike with not-being”, he is referring to the Platonists. Aquinas explains:

“He says that the Platonists also held a certain duality on the part of matter, namely, the great and the small. But this duality is different from that of Aristotle. For Aristotle held that the duality was matter and privation, which are one in subject but different in nature [ratio]. But the Platonists did not hold that one of these is privation and the other matter, but they joined privation to both, i.e., to the great and the small. They either took both of them together, not distinguishing in their speech between the great and the small, or else they took each separately. Whence it is clear that the Platonists, who posited form and the great and the small, held three completely different principles than Aristotle, who posited matter and privation and form. The Platonists realized more than the other ancient philosophers that it is necessary to suppose some one nature for an natural forms, which nature is primary matter. But they made it one both in subject and in nature [ratio], not distinguishing between it and privation. For although they held a duality on the part of matter, namely, the great and the small, they made no distinction at all between matter and privation. Rather they spoke only of matter under which they included the great and the small. And they ignored privation, making no mention of it” (Lectio 15.133) [6].

The Platonists held that the “Great and Small” are the material principles of things, that in which the participation of the forms are instantiated in. Aristotle held, as we’ve seen, that matter and privation are one in subject and different in nature. But the Platonists, we’re told here, apparently held that in some sense the very nature of the Great and Small is one with privation, or somehow contains privation, and so they “identify their Great and Small alike with not-being”. Since, for them, the Great and Small are the material principles of things, and since they contain privation, then matter and privation are in some sense one, undistinguished. As Aristotle points out, the Platonists recognized that there must be “some underlying nature” to the forms, which is matter, but they made the matter one in nature. Their duality of matter is just in terms of the Great and Small, not in terms of matter and privation, so “the effect is the same” as if they just lacked an account of duality altogether (which is necessary to explain change).

Next, where Aristotle says “For the one which persists is a joint cause, with the form, of what comes to be”, he’s referring back to the principles which he has earlier established (see especially chapter 7). The “one which persists” is the matter, the underlying subject of the change which survives the change, while the form is what comes to be. He compares the matter to a mother, since “just as a mother is a cause of generation by receiving, so also is matter” (Lectio 15.135) [7]. Aristotle’s next comment is intriguing: “But the negative part of the contrariety may often seem, if you concentrate your attention on it as an evil agent, not to exist at all”. This reference to the privation as a kind of “evil” is extremely significant, because it is a seed of a much larger theory of evil which would come to be adopted and developed by many Christian philosophers in later centuries including Augustine but especially Aquinas. Relevant for us here, however, is just the idea that a privation of a thing is “altogether non-being, since it is nothing other than the negation of a form in a subject, and is outside the whole being” [8]. Privation is a principle of change, as he’s explained before, but it is in a sense a mere conceptual principle, since it has no real existence of its own. And so “The argument of Parmenides that whatever is other than being is non-being, has a place in regard to privation, but not in regard to matter, as the Platonists said” [9]. In other words, privation is other than being and is really non-being; but matter is, in a sense, “other than” actual being, but is not non-being simply, since it is potency.

Aristotle continues:

“For admitting with them that there is something divine, good, and desirable, we hold that there are two other principles, the one contrary to it, and the other such as of its own nature to desire and yearn for it. But the consequence of their view is that the contrary desires its own extinction. Yet the form cannot desire itself, for it is not defective; nor can the contrary desire it, for contraries are mutually destructive. The truth is that what desires the form is matter, as the female desires the male and the ugly the beautiful–only the ugly or female not per se but per accidens(192a17-24) [10].

Basically, what Aristotle is getting at is this: form is being, and being is good and desirable. This both Aristotle and the Platonists agree upon. Aquinas expands upon this point a bit:

“Form is something divine and very good and desirable. It is divine because every form is a certain participation in the likeness of the divine being, which is pure act. For each thing, insofar as it is in act, has form. Form is very good because act is the perfection of potency and is its good; and it follows as a consequence of this that form is desirable, because every thing desires its own perfection” [11].

That is more than needs to be said here, however. Aristotle just points out that form is being or act, and that form is one of the principles of change. There are two others, again as he’s already established. One is contrary to the form, which is privation. The other, he says, is “such as of its own nature to desire and yearn for it”. This is matter. The desire he mentions here is not some kind of conscious or mental desire, but the natural, automatic desire of things for their ends. Matter is a potency for something, and so is naturally directed towards that which is its object. But the view of the Platonists, he insists, reduces to an impossibility. For “the consequence of their view is that the contrary desires its own extinction”. In other words, since privation is the contrary of form, and since contraries necessarily cannot exist together (something cannot both be white and not-white at the same time), then if, as the Platonists posit, privation and matter are the same, and matter naturally seeks form, then this must mean that a privation naturally seeks that which is its opposite/contrary, which is necessarily its own “extinction”. As Aquinas puts it, “This involves the absurdity that a contrary seeks its own corruption, which is absurd” (Lectio 15.136) [12]. Aristotle furthers his defense by pointing out that “form cannot desire itself, for it is not defective”. This is comparable to Parmenides’s statement that being cannot come from being, because being already is. A doctor cannot “change” into a doctor, since he already is a doctor. So some form which actually exists does not desire “itself”, since it is already there. But “nor can the contrary desire it, for contraries are mutually destructive”. A contrary does not seek the form of which it is a privation, since that would be to seek its own termination and non-existence. No, what must be the case is that the principle of matter is that which desires the form, and this means that the three principles must actually be distinct; matter and privation cannot be one. But, Aquinas is careful to point out, privation does “seek” form per accidens, insofar as that matter which seeks form necessarily includes the privation of that form, but is not identical to that form. He writes:

“It is clear, therefore, that matter, which seeks form, is other in nature [ratio] from both form and privation. For if matter seeks form according to its proper nature, as was said, and if it is held that matter and privation are the same in nature [ratio], it follows that privation seeks form, and thus seeks its own corruption, which is impossible. Hence it is also impossible that matter and privation be the same in nature [ratio]. Nevertheless, matter is ‘a this’, i.e., something having privation. Hence, if the feminine seeks the masculine, and if the base seeks the good, this is not because baseness itself seeks the good, which is its contrary; rather it seeks it accidentally, because that in which baseness happens to be seeks to be good. And likewise femininity does not seek masculinity; rather that in which the feminine happens to be seeks the masculine. And in like manner, privation does not seek to be form; rather that in which privation happens to be, namely, matter, seeks to be form” [13].

Aristotle continues:

“The matter comes to be and ceases to be in one sense, while in another it does not. As that which contains the privation, it ceases to be in its own nature, for what ceases to be–the privation–is contained within it. But as potentiality it does not cease to be in its own nature, but is necessarily outside the sphere of becoming and ceasing to be. For if it came to be, something must have existed as a primary substratum from which it should come and which should persist in it; but this is its own special nature, so that it will be before coming to be. (For my definition of matter is just this–the primary substratum of each thing, from which it comes to be without qualification, and which persists in the result.) And if it ceases to be it will pass into that at the last, so it will have ceased to be before ceasing to be” (192a25-34) [14].

When change takes place, says Aristotle, in one sense matter itself undergoes corruption, but in another sense it doesn’t. As we’ve said, matter contains privation. In a change, privation is what is corrupted, what “ceases to be”, and so insofar as matter contains privation, it too undergoes a kind of corruption during the process of change. But “in itself, insofar as it is a certain being in potency, it is neither generated nor corruptible” (Lectio 15.139) [15]. Or as Aristotle puts it, “In its own nature . . . [it is] necessarily outside the sphere of becoming and ceasing to be”. For all becoming requires an underlying substratum in which the change can take place, and which will survive the change (as established earlier). But that just is matter: matter is the fundamental underlying substratum. That is the very definition of matter given by Aristotle: “the primary substratum of each thing, from which it comes to be without qualification, and which persists in the result”. So if matter itself were to change, it would have to exists before it exists, in order for it to come into existence, which is impossible. “And in like manner”, says Aquinas, “everything which is corrupted is resolved into primary matter” [16], since to be corrupted is to lose form, and that which lacks form is just matter. Thus if matter itself were to be corrupted, it would have to lose its “form”. But primary matter by definition has no form, so if it somehow could it exist on its own, it would already be corrupted. In simpler terms, primary matter cannot be corrupted, since to be corrupted is to lose form, but primary matter by definition has no form to begin with which it could lose. So, to summarize, in the process of change, matter itself changes just insofar as the certain privation which it contains is changed; but in itself, it never is generated or corrupted.

And so Aristotle concludes Book One:

“The accurate determination of the first principle in respect of form, whether it is one or many and what it is or what they are, is the province of the primary type pf science; so these questions may stand over till then. But of the natural, i. e. perishable, forms we shall speak in the expositions which follow. The above, then, may be taken as sufficient to establish that there are principles and what they are and how many there are. Now let us make a fresh start and proceed” (192a34-192b5) [17].

As he said at the beginning, Physics is the study of mutable being, or changing being, and so he has focused mainly on the principles of matter and privation. But the principle of form, he now says, is much more properly treated in “the primary” science, or “first philosophy” which is metaphysics. In the rest of the Physics, he tells us, he will treat of the natural/perishable forms.

At the very beginning of Book One, Aristotle set out to provide an explanation of change, and at long last he has completed exactly that. Along the way he has responded to views of a good many of the other ancient philosophers who went before him but erred, failing to adequately establish a framework for the philosophy of physics, which he now has done. He has argued for there being three main principles of change in nature: privation, matter, and form, and associated with them his history-altering distinction between being as act and being as potency.


It has taken over five months to complete my exposition/commentary of Book One of the Physics. I have thoroughly enjoyed the process. It is one thing to read Aristotle, but to dive deep and write explanatory commentary is a whole other experience, and has deeply enriched my own appreciation/understanding. I recognize these Reading Aristotle posts might be tedious and less exciting than others, but I think there’s great value in it. In any case, I’ll continue to write them, at least for my own sake. Of course, I also completely recognize that I cannot even begin to hope to get through all or even a good number of his writings. After all, the Physics alone has seven more books, and it’s much shorter than the Metaphysics. As such, I may not continue my series in order; I may “bounce around” to different works from time to time. I also plan to be writing a general outline of the arguments in Book One of the Physics before moving on to Book Two, to provide an easy reference.

Until then, thanks for reading.



[1].  McKeon, Richard, editor. The Basic Works of Aristotle. New York: Random House, Inc, 1941. Print, 234-235.

[2].Thomas Aquinas. Commentary on Aristotle’s Physics. Books I-II translated by Richard J. Blackwell, Richard J. Spath & W. Edmund Thirlkel Yale U.P., 1963. <>.

[3]. Ibid.

[4]. McKeon. Aristotle. 235.

[5]. Aquinas. Commentary.

[6]. Ibid.

[7]. Ibid.

[8]. Ibid.

[9]. Ibid.

[10].McKeon. Aristotle. 235.

[11]. Aquinas. Commentary.

[12]. Ibid.

[13]. Ibid.

[14]. McKeon. Aristotle. 235.

[15]. Aquinas. Commentary.

[16]. Ibid.

[17]. McKeon. Aristotle. 235-236.

Header image in the Public Domain in the United States, taken from Wikimedia Commons:


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