Reading Aristotle: Physics 1.7: The Principles of Nature

In Physics 1.6, Aristotle established that the number of fundamental principles of nature must be three. He begins 1.7:

“We will now give our own account, approaching the question first with reference to becoming in its widest sense: for we shall be following the natural order of inquiry if we speak first of common characteristics, and then investigate the characteristics of special cases” (Physics 1.7, 189b30-32) [1].

Since he is searching for the underlying principles of nature, and since “nature” itself to Aristotle is the principle of motion of things–“a source or cause of being moved and of being at rest in that to which it belongs primarily” (2.1, 192b22-23) [2]–then to understand the underlying principles themselves we must examine the motion of things. And so here he states that he will consider “becoming in its widest sense”, as it applies to all things commonly, before then investigating individual cases.

“We say that one thing comes to be from another thing, and one sort of thing from another sort of thing, both in the case of simple and complex things. I mean the following. We can say (1) the ‘man becomes musical’, (2) what is ‘not-musical becomes musical’, or (3) the ‘not-musical man becomes a musical man’. Now what becomes in (1) and (2)–‘man’ and ‘not musical’–I call simple, and what each becomes–‘musical’–simple also. But when (3) we say the ‘not-musical man becomes a musical man’, both what becomes and what it becomes are complex” (1.7, 189b32-190a4) [3].

Here, Aristotle is getting at something like this: when we say that a man becomes musical, that which changes (the man) and that into which he becomes (musical) are both “simple”, i.e. they only make reference to some one specific thing or aspect. Now a man is obviously a substance, and “musical” is obviously an accident (quality/characteristic). But in saying that the man becomes musical, we are not claiming that a substance itself becomes an accident, which would just be impossible and absurd (the man doesn’t turn into “musicalness”, he just gains it as an accident).  We actually seem to be meaning the same thing as (3), that a non-musical man becomes a musical man, but in our statement we are only make reference to one aspect for each.

Aquinas comments:

“In any coming-to-be one thing is said to come to be from another thing with reference to coming to be in regard to substantial being [esse], or one comes to be from another with reference to coming to be in regard to accidental being [esse]. Hence every change has two termini. The word ‘termini’, however, is used in two ways, for the termini of a production or mutation can be taken as either simple or composite” (Lectio 12.101) [4].

In (1), we say the man (the referent being the substance) becomes musical (the referent switching to the accident). Thus each referent itself is simple. Every change of this sort actually involves two things, or “has two termini” as Aquinas put it: the substance and the accident. Every change involves a relation between the two termini. If we say that a man becomes musical, we are referring simply to a relation between substance and its accident, where the accident changes. The substance doesn’t change, for the man remains a man; only the accident changes in the substance. But the statement of (1) includes both as referents. If we say that “the non-musical becomes musical”, we are similarly only referring to the termini simply. In this case, however, we do not make any reference to the substance. Obviously there is a substance involved, since “musicalness” cannot exist on its own, independently of some subject which has it as a quality. But this statement only makes reference to what in the substance is actually changing: the accidents.

The third statement, however, is “complex”. For both referents in this case include both termini. The “that-which-changes” refers both to the substance and the accident; and the “that-which-it-becomes” likewise refers both to the substance and the accident.

Aristotle continues:

“As regards one of these simple ‘things that become’ we say not only ‘this becomes so-and-so’, but also ‘from being this, comes to be so-and-so’, as ‘from being not-musical comes to be musical’; as regards the other we do not say this in all cases, as we do not say (1) ‘from being a man he came to be musical’ but only ‘the man became musical'” (1.7, 190a5-8) [5].

He here seems to be pointing out that, in some cases of simple statements, we can refer to the statement in one of two ways. Either we can say, “this pile of bricks becomes a house”; or we can reverse the statement, as it were, and say: “from being a pile of bricks, comes to be a house”. But notice that in both of these, the simple referents are both only substances. We could also formulate the statement in both ways in terms of accidents. We could say, for instance, “the short becomes tall,” and “from being short comes to be tall”. But this, Aristotle points out, only works in simple statements wherein both referents are the same termini. In a statement where one referent is a substance and the other is an accident, we can’t use the “twofold mode of speech” [6], as Aquinas calls it. We can say “the man became tall”, but not “from being a man he came to be tall”. Nor, would it seem, can we say either that “the tall became man” or that “from being tall he came to be a man”, for neither of these, due to the inherent limitations of language, make clear what exactly is changing. When we say “the man becomes musical”, it is just assumed that by “musical” one means “a musical man”, so that it is obvious that what has changed is the accident, from non-musical to musical. In fact, in English as well as Latin and Greek, when an adjective stands alone as such but is meant to be taken as implying a noun, it is called a substantive adjective, showing that it refers to some substance which has the attribute. In saying “the not-musical becomes musical”, it is clear that both referents are substantive adjectives, and, although this sentence alone is not enough to tell us what substance exactly is involved, it is clear enough to tell us that the accidents in that subject are what is changing. But saying “the tall became man”, due to linguistic limitation, just doesn’t identify sufficiently what is changing. It is ambiguous whether it means to say that some tall man became a short man, or whether some other tall thing became a man, and that itself still leaves open whether the man it becomes is tall or short.

Taking time to labor over such trivial semantics may seem meaningless, but it becomes extremely important to recognize what our speech implies as we progress in discussing the very nature of change.

“When a ‘simple’ thing is said to become something, in one case (1) it survives through the process, in the other (2) it does not. For the man remains a man and is such even when he becomes musical, whereas what is not musical or is unmusical does not continue to exist, either simply or combined with the subject” (1.7, 190a8-12) [7].

Change, to the ancients, was such a difficult concept to grasp because it seemed to require, in some sense, being coming into existence from non-being, which they regarded as just blatantly impossible and incoherent. This is what Aristotle is trying to make sense of throughout the Physics. Here he points out that in some cases of change, there is something that “survives through the process” of transformation. When a man becomes tall, he remains a man, even if some aspect/characteristic of him has been altered. But in other cases, it seems that this is not so. For in the second original statement from above, in which the “not-musical becomes musical”, there is nothing about the first referent that remains or survives the process into the second referent. “Not-musical” and “musical” are, by definition, complete contraries; they cannot exist together. What is not-musical passes completely away, and what is musical comes to be completely; there is no possible “mixture” of the two. Notice that this is also the case when the simple accident is “combined with the subject”, as in the complex statement. When the “not-musical man” becomes the “musical man”, the first referent, as it is in itself, does not survive. The “man” as substance may survive, but the whole “not-musical man” in its entirety does not; it becomes the “musical man”. Thus only in statements wherein one referent is a simple substance and one includes an accident is it true that the thing itself survives the process of change, since what we are referring to, the substance, does not pass away.

“These distinctions drawn, one can gather from surveying the various cases of becoming in the way we are describing that, as we say, there must always be an underlying something, namely that which becomes, and that this, though always one numerically, in form at least is not one. (By that I mean that it can be described in different ways.) For ‘to be man’ is not the same as ‘to be unmusical’. One part survives, the other does not: what is not an opposite survives (for ‘man’ survives), but ‘not-musical’ or ‘unmusical’ does not survive, nor does the compound of the two, namely ‘unmusical man'” (1.7, 190a13-20) [8].

But, even in those cases in which what we are referring to as a whole does not survive, it must be, argues Aristotle, that there is always something “underlying” the change; something that survives. Consider the three original statements: 1) In “the man becomes musical”, what is changing is the accident, “musical”, but, as we’ve said, accidents cannot exist on their own; there must be something that has the accident. So if it is the accident which changes, what has the accident stays the same, at least in itself. For the man who becomes musical remains a man, and does not change into something else that is not a man just by virtue of becoming musical. 2) In “the not-musical becomes musical”, what is changing is again the accident; and even though there is no mention of a substance, it is clear that there must be some underlying substance in which the accidents change. 3) In “the not-musical man becomes a musical man”, what we are referring to as a whole changes, but only because the “whole” in this case includes both substance and its accidents, and it is the accidents within the substance which change; but the substance remains essentially itself.

He calls the underlying subject the “that which becomes” because it as a whole is one numerically, and it is this that actually undergoes change; even though one part of it survives and one does not. In other words, when a man changes from being not-musical to being musical, the man himself as a whole actually changes; but part of the man does survive the change, namely the part of the man that is essentially man, regardless of its accidents. It is “one numerically”, says Aristotle, because even though a “musical man” has many different parts/aspects of his being, he is still one thing. But it differs “in form”, meaning that, conceptually at least, we can separate the substance from its accidents. Being a man is not identical to being musical; after all, many men are not musical, and other things besides men can be musical (instruments, songbirds, etc.). When this thing changes, the part that does not survive is the “opposite”; the “not-musical” turns into its opposite, the “musical”. But from one end of the change to the other, what stays the same does not become its opposite. Man does not become “not-man” when a not-musical man becomes a musical man.

“We speak of ‘becoming that from this’ instead of ‘this becoming that’ more in the case of what does not survive the change–‘becoming musical from unmusical’, not ‘from man’–but there are exceptions, as we sometimes use the latter form of expression even of what survives; we speak of ‘a statue coming to be from bronze’, not of the ‘bronze becoming a statue’. The change, however, from an opposite which does not survive is described indifferently in both ways, ‘becoming that from this’ or ‘this becoming that’. We say both that ‘the unmusical becomes musical’, and that ‘from unmusical he becomes musical’. And so both forms are used of the complex, ‘becoming a musical man from an unmusical man’, and ‘an unmusical man becoming a musical man'” (1.7, 190a21-31) [9].

Similarly to his above explanation, he notes that when we use the structure “becoming that from this” as opposed to “this becoming that”, we more often are referring to what does not survive a change. So we say, “he is becoming old from being young”, but not “he is becoming old from being a man”. He grants that we sometimes do use this structure when referring to both subject and opposite, as when we say “a statue being made from bronze”, but, again, we wouldn’t say “the bronze becomes a statue” (Although this latter sentence might make sense in English, if we compare it to the previously used “the tall becomes a man”, we can see his point. Saying “the bronze becomes a state” doesn’t make clear what the bronze previously was). His point here is that, when referring to subjects, it is more proper to say “this becomes x” than to say “from x, becomes this”. But when referring just to the opposites, we can say either “non-x becomes x”, or “from non-x, becomes x”. And, as such, we can use both for complex statements as well.

The implication of this, as Aquinas draws out, seems to be used as further support for concluding that subject and opposite are at least conceptually distinct.

Aristotle goes on:

“But there are different senses of ‘coming to be’. In some cases we do not use the expression ‘come to be’, but ‘come to be so-and-so’. Only substances are said to ‘come to be’ in the unqualified sense. Now in all cases other than substance it is plain that there must be some subject, namely, that which becomes. For we know that when a thing comes to be of such a quantity or quality or in such a relation, time, or place, a subject is always presupposed, since substance alone is not predicated of another subject, but everything else of a substance. But that substances too, and anything else that can be said ‘to be’ without qualification, come to be from some substratum, will appear on examination. For we find in every case something that underlies from which proceeds that which comes to be; for instance, animals and plants from seed” (1.7, 190a32-190b4) [10].

There are different ways in which change occurs. When a man grows from short to tall, he still stays a man, stays essentially the same. Thus in that case he only undergoes accidental change; but in some cases there is substantial change. A substantial change would be when the substance itself changes: for example, when an animal dies, it goes from being a living organism to being only a corpse. Or, consider when independent oxygen and hydrogen molecules combine to form a completely new thing: water. Before the combination of hydrogen and oxygen, the water molecule does not exist; so we say that the water “comes to be” unqualifiedly (not necessarily coming to be from nothing, just coming to be in the sense that the form of water comes to be, when it previously was not). When a substance comes to be, it does not do so in some other substance; for as Aristotle maintains (and defends in his book Categories), “substance alone is not predicated of another subject, but everything else of substance”. So all other non-substantial, or accidental, change, occurs in some substance; but the coming to be of a substance itself does not.

But, in fact, Aristotle will argue, even though a substance does not come to be in another substance, it must itself have some substratum in which the change takes place. For, otherwise, the change would literally be something coming from nothing, which is impossible.

“Generally, things which come to be, come to be in different ways: (1) by change of shape, as a statue; (2) by addition, as things which grow; (3) by taking away, as the Hermes from the stone; (4) by putting together, as a house; (5) by alteration, as things which ‘turn’ in respect of their material substance. It is plain that these are all cases of coming to be from a substratum” (1.7, 190b5-9) [11].

Here he just lists explicitly the different ways in which change can occur. First, the external shape of something can change, such as when a statue is sculpted. Second, by addition, as when anything increases in any respect; and third is the same except by subtraction, when anything decrease. Fourth is composition, when different parts are put together into a single structure. And finally, fifth, when something’s “matter is changed” (Lectio 12.108) [12]. But in all these cases, there is an underlying substratum/subject in which the change takes place.

“Thus, clearly, from what has been said, whatever comes to be is always complex. There is, on the one hand, (a) something which comes into existence, and again (b) something which becomes that–the latter (b) in two senses, either the subject or the opposite. By the ‘opposite’ I mean the ‘unmusical’, by the ‘subject’ ‘man’, and similarly I call the absence of shape or form or order the ‘opposite’, and the bronze or stone or gold the ‘subject'” (1.7, 190b10-16) [13].

So, even though our statements can be simple in structure, in reality change is always complex, i.e. it always involves both subject and opposite. So, in conclusion of everything that has been said, Aristotle establishes that in any change there are three aspects. First, that “which comes into existence.” Aquinas calls this the “terminus”, or the “that at which the coming to be is terminated” (Lectio 12.109) [14]. So when an acorn becomes an oak tree, the oak tree is the “terminus” of the change; the that-into-which the acorn changed. Then there is the “something which becomes that”, or what it is that ultimately becomes the terminus. This would be the acorn. But this itself is further divided into two aspects: the subject and the opposite. In the case of a not-musical man who becomes musical, “man” is the subject and “not-musical” is the opposite, and “musical man” is the terminus. When crafting a statue, the stuff the statue is sculpted out of is the subject, the “absence of shape” is the opposite, and a “shaped statue” is the terminus.

“Plainly then, if there are conditions and principles which constitute natural objects and from which they primarily are or have come to be–have come to be, I mean, what each is said to be in its essential nature, not what each is in respect of a concomitant attribute–plainly, I say, everything comes to be from both subject and form. For ‘musical man’ is composed (in a way) of ‘man’ and ‘musical’: you can analyse it into the definitions of its elements. It is clear then that what comes to be will come to be from these elements” (1.7, 190b16-23) [15].

The “conditions” and “principles” of a thing are its underlying causes/elements, as he has explained throughout the Physics. But for everything in nature, these principles seem to include subject and form. Aquinas explains further:

“Those things into which the definition of a thing is resolved are the components of that thing, because each thing is resolved into the things of which it is composed. But the definition [ratio] of that which comes to be according to nature is resolved into subject and form. For the definition [ratio] of musical man is resolved into the definition [ratio] of man and the definition [ratio] of musical. For if anyone wishes to define musical man, he will have to give the definitions of man and musical. Therefore, that which comes to be according to nature both is and comes to be from subject and form” (Lectio 13.11) [16].

So when a “musical man” comes to be, the form of “musical” comes to be in the subject man. The subject is that in which the change takes place; the form is what becomes, what is predicated of the subject. We might relate the use of form here to the “terminus” above. The subject here includes the opposite/privation, since if we say “the man becomes musical”, the “man” is obviously implied to be at first non-musical, and then to change into a musical man.

Aristotle continues:

“Now the subject is one numerically, though it is two in form. (For it is the man, the gold–the ‘matter’ generally–that is counted, for it is more of the nature of a ‘this’, and what comes to be does not come from it in virtue of a concomitant attribute; the privation, on the other hand, and the contrary are incidental in the process.) And the positive form is one–the order, the acquired art of music, or any similar predicate” (1.7, 190b23-27) [17].

As mentioned above, a subject is one–a “musical man” is just one being. But it is two “in form”, or, as Aquinas says, in “species and nature” (Lectio 13.112) [18]. For in a musical man, being “musical” and being “man” are conceptually two different things. But, as he says, it is the man that is actually “counted”, so that we say a musical man is one being. Now, as he’s said, the principles of what come to be according to nature are the subject and form. But when something comes to be, it does not do so “in virtue of a concomitant attribute”. In other words, when a man becomes musical, he does not become musical in virtue of him being short or tall, or having brown or black hair. These attributes are non-essential to the actual change in question. But what is essential to the change are the privation and the contrary–from non-musical to musical. The “positive form” is the form that becomes from some privation, as in the examples just given.

Now, here, Aquinas contends that subject and form are per se principles of change, and privation is a per accidens principle. His point seems to be this: when a man becomes musical, the man originally is “non-musical”. But “non-musical” is merely a privation; it is not some actual, positively existent aspect. It can only be defined in relation to some real, positive attribute, e.g. the musical. When the change takes place, it cannot occur by virtue of non-musicalness, since non-musicalness just isn’t a positive actuality that can “effect” anything. The change comes by virtue of the man himself; so his original “non-musicalness” is just an accident feature of the change. Aquinas writes further:

“Hence it must be said that matter is never without privation. For when matter has one form, it is in privation of some other form. And so while it is coming to be that which it becomes (e.g., musical man), there is in the subject, which does not yet have the form, the privation of the musical itself. And so the per accidens principle of a musical man, while he is coming to be musical, is the non-musical. For he is a non-musical man while he is coming to be musical. But when this latter form has already come to him, then there is joined to him the privation of the other form. And thus the privation of the opposite form is a per accidens principle of being. It is clear, therefore, according to the opinion of Aristotle that privation, which is posited as a per accidens principle of nature, is not a capacity for a form, nor an inchoate form, nor some imperfect active principle, as some say. Rather it is the very absence of form, or the contrary of form, which occurs in the subject” (Lectio 13.113) [19].

Back to Aristotle:

“There is a sense, therefore, in which we must declare the principles to be two, and a sense in which they are three; a sense in which the contraries are the principles–say for example the musical and the unmusical, the hot and the cold, the tuned and the untuned–and a sense in which they are not, since it is impossible for the contraries to be acted on by each other. But this difficulty also is solved by the fact that the substratum is different from the contraries, for it is itself not a contrary. The principles therefore are, in a way, not more in number than the contraries, but as it were two, nor yet precisely two, since there is a difference of essential nature, but three. For ‘to be man’ is different from ‘to be unmusical’, and ‘to be unformed’ from ‘to be bronze'” (1.7, 190b28-191a3) [20].

This refers back to chapter six, in which the number of principles was established, but Aristotle admitted that there is some difficulty in determining whether they are two or three. For, he argued, the two contraries must be principles, but, since contraries by definition cannot act on each other, there must be some underlying substratum, which is a third principle.

Here he says there is a sense in which we can hold the contraries as principles, since when something changes, it is in terms of its contraries that it does so (from short to tall). But in another sense, we cannot hold the contraries to be the principles of a change, since they are insufficient to account for the change without some substratum. In conclusion he arrives at the fact that there must be three principles: the subject, the form, and the privation, the latter two of which are contraries.

“We have now stated the number of the principles of natural objects which are subject to generation, and how the number is reached: and it is clear that there must be a substratum for the contraries, and that the contraries must be two. (Yet in another way of putting it this is not necessary, as one of the contraries will serve to effect the change by its successive absence and presence.)” (1.7, 191a3-7) [21].

So it is necessary to posit two contraries in the substratum. But, in a sense, since one of the contraries is a mere privation, we could just refer to one contrary.

“The underlying nature is an object of scientific knowledge, by an analogy. For as the bronze is to the statue, the wood to the bed, or the matter and the formless before receiving form to any thing which has form, so is the underlying nature to substance, i.e. the ‘this’ or existent. This then is one principle (though not one or existent in the same sense as the ‘this’), and the definition was one as we agreed; then further there is its contrary, the privation. In what sense these are two, and in what sense more, has been stated above. Briefly, we explained first that only the contraries were principles, and late that a substratum was indispensable, and that the principles were three; our last statement has elucidated the difference between the contraries, the mutual relation of the principles, and the nature of the substratum” (1.7, 191a8-19) [22].

When a man becomes musical, the subject is that in which the change takes place (man), and the “form” is that which becomes (musical). This, as we said, was just a change in the accidents of some substance. But at times there is a change in the substance itself; for example, a tree is chopped down and its wood is made into a bed. Let’s consider the bed as a substance (even though in reality it is an artifact). When a man becomes musical, musical comes to be in the man from non-musical. If a bed became red from being brown (by virtue of being painted), the red would come to be from non-red (which in this case would be brown). But when the bed itself comes to be, it comes to be from non-bed, but in what does it come to be? What is its subject? The answer is the underlying wood, the matter from which it is formed. So when a substance comes to be, it has some underlying nature/matter as its subject of change, and this is one principle. (He notes that it is not “one” or “existent” in the same sense as a substance, since, as will be argued as the Physics progresses, primary matter cannot exist on its own without a substance). Then there are the contraries. Whereas before, the “form” which came to be was merely an accident of some substance, here the form that comes to be is the substance itself. But since in this case the contrary to having the form of substance is just having no form, we only need make reference to one contrary. There is no really existent contrary “not-bed”, rather, there is just having the form of bed, which is either present or absent in the underlying subject. So, even though conceptually there are three principles, we can speak of just two and still make a full account of the change.

He finishes:

“Whether the form or the substratum is the essential nature of a physical object is not yet clear. But that the principles are three, and in what sense, and the way in which each is a principle, is clear. So much then for the question of the number and the nature of the principles” (1.7, 191a19-22) [23].

We will next turn to chapter 8, the penultimate chapter in Book 1.



[1]. McKeon, Richard, editor. The Basic Works of Aristotle. New York: Random House, Inc, 1941. Print, 230.

[2]. Ibid., 236.

[3]. Ibid., 230.

[4]. 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. <>. Lectio 12.101.

[5]. McKeon. Aristotle. 230.

[6]. Aquinas. Commentary. Lectio 12.102.

[7]. McKeon. Aristotle. 230.

[8]. Ibid.

[9].  Ibid., 231.

[10]. Ibid.

[11]. Ibid.

[12]. Aquinas. Commentary. Lectio 12.108.

[13]. McKeon. Aristotle. 231.

[14]. Aquinas. Commentary. Lectio 12.109.

[15]. McKeon. Aristotle. 231-232.

[16]. Aquinas. Commentary. Lectio 13.111.

[17]. McKeon. Aristotle. 232.

[18]. Aquinas. Commentary. Lectio 13.112.

[19]. Ibid. 13.113.

[20]. McKeon. Aristotle. 232.

[21]. Ibid.

[22]. Ibid., 232-233.

[23]. Ibid., 233.

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


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