Jacques Maritain Center: Thomistic Institute

Sources of St. Thomas' Teaching on Prime Matter
Or, Albert and Thomas on Matter

By Steven Baldner
Thomistic Institute, July 14-21, 2000

The theme of this year's Thomistic Institute is that of the sources of St. Thomas' thought. I have chosen to give attention to Thomas' doctrine of matter, as I have done at a previous meeting of this Institute, and, also as before, I am particularly concerned to bring out more clearly the relationship between Thomas and his teacher, St. Albert the Great. No one did more in the thirteenth century than these two Dominicans to bring genuinely Aristotelian doctrine into scholastic philosophical and theological discussions. It is sometimes tempting, in fact, to think that Thomas and Albert speak on all important philosophical matters with one voice, however much there might be two quite distinct accents, one being rather decidedly Germanic. I think, however, that we should resist this temptation, for Albert's position on matter, as I hope to show, is certainly Aristotelian but is an Aristotelian position laced with certain traces of the Arabic commentators, especially traces of the Commentator. Thomas was initially attracted to Albert's position, but in his maturity he came to reject certain tenets in Albert that were Averroistic.

In this paper I shall focus on two problems that were very difficult for the scholastic philosophers to explain. First, there is the problem of explaining the heavenly bodies, in contrast to the earthly bodies. Until the seventeenth century, everyone recognized that the matter of the bodies outside of our atmosphere - the moon, the sun, the plants, the stars - was somehow different from the matter out of which things are made on our earth. Explaining this difference, however, proved to be very difficult. Second, there is the problem, which I dealt with two years ago before this audience,(1) of explaining how it is that elements can remain in compounds. To explain this problem successfully requires showing how something can undergo a substantial change and yet somehow remain what it is in spite of that substantial change. On both of these problems Albert manifests a certain Averroist tendency, namely, the introduction of an explanatory form that is neither substantial nor accidental. In the case of the heavenly bodies, he introduces a "form of corporeity" (forma corporeitatis) to explain the difference between earthly and heavenly matter, and this "form of corporeity" is neither substantial nor accidental. In the case of the elements, Albert holds that the elemental forms are neither substantial nor accidental but some transitory, tertium quid. These positions of Albert, tinged with Averroism, were attractive to the young Thomas. Later, however, Thomas came to reject these positions as being inconsistent with a fully Aristotelian understanding of form and matter.(2)

First, then, let us consider the problem of explaining the matter of the heavenly bodies. The problem is the following. The empirical evidence seemed to show unambiguously that the heavenly bodies were incorruptible. The stars and the planets certainly change in that they are perpetually moving, but their motion is only a motion in place. They are never altered in quality, they never change in quantity, and they are never generated or corrupted. For as long as the universe exists, the heavenly bodies have existed unchanged, except for their perfectly regular and circular motions. By contrast, of course, the bodies we know immediately here on earth are always changing in all possible ways: in place, in quality, in quantity, and in being. It seems inescapable, therefore, to conclude that the matter of the heavenly bodies is a different sort of matter from that which we know down here. In fact, the heavenly bodies were recognized to be not made of the four elements out of which all terrestrial substances are made but to be a fifth sort of element, called "ether". Now, these ethereal substances are incorruptible, but why are they so? They are seemingly material substances, and all material substances are composed of prime matter and substantial form. But prime matter is a radical potency to any substantial form. It would seem that by virtue of their composition as material substances they must be liable to destruction, and yet we know on good empirical grounds that they are completely indestructible. How, then, do we explain the incorruptibility of the heavenly bodies? Such was the problem faced by Albert and by Thomas. What did each say to solve this problem?

Albert's position on this problem did not change over his long career, so far as I can tell. In his paraphrase of Aristotle's De caelo (book 1, tract. 3, chapter 4), a work written in the 1250s, Albert gives a complete account of how heavenly bodies differ from terrestrial. First, he says, we must be clear that "prime matter" is a term used to indicate the fundamental potency of a substance. This potency is pure potency such that in itself prime matter has absolutely no actual form.(3) At its most fundamental, this potency is a receptivity for form, and that is why prime matter cannot be a composite of something material and something formal, for if it were it would by that very fact not be receptive of form. In other words, as Albert says, the pure receptivity of prime matter implies that there can be only one substantial form for any substance. If prime matter is determined by one substantial form, it cannot then also be determined by some other substantial form.

Here let me comment that what Albert has said thus far about prime matter expresses very well what his student, Thomas, would also hold. Prime matter is a purely potential principle of receptivity, is not actual in any way, cannot be a thing in itself, and can be determined by one and only one substantial form. So far so good. Albert's position, however, becomes more complicated when he distinguishes the heavenly from the earthly bodies.

There are, says Albert, fundamentally two different kinds of substantial form, the kind of substantial form that belongs to the heavenly bodies and the kind that belongs to the earthly.(4) First, let us consider what Albert says about the earthly bodies. The substantial forms of earthly bodies are the acts of bodies that are divisible, quantitatively determinate, and finite. These substantial forms realize their operations entirely in and through the bodies of which they are the primary actuality. But there is a difficulty in explaining how it is that prime matter is receptive of substantial form, because prime matter must be divisible and subject to dimensions in order to receive the form of an earthly substance. Prime matter, however, in itself, is not divisible nor subject to quantitative dimensions, for if it were, it would have some sort of actuality and it would be, as we have seen, not prime matter any more. There must, therefore, says Albert, be some other form that renders prime matter divisible and subject to dimensions, and this form must belong to the substance before it receives its substantial form. That is to say, the prime matter of terrestrial substances requires a "form of corporeity" (forma corporeitatis) to allow the matter to receive the substantial form of such substances. Let me quote Albert.

Since matter, being completely indivisible, cannot be divided into quantitative parts subject to different forms, it is necessary that, in order to receive a form that is the act of a body, matter must first become capable of receiving three dimensions. Matter must be capable of receiving dimensions, but it must not have determinate dimensions, for if it did, it would itself corrupt in every generation and corruption. For this reason matter receives first a form, which is the form of indeterminate dimensions, through the mediation of which matter becomes divisible into parts and able to receive substantial form. This corporeity is a form that is common to all forms that matter receives. Hence, the corporeity of matter, which is like a first form before all other forms that are perfections of bodies, remains in matter and is never separated from it in any corporeal change.(5)

Albert is introducing here an Averroistic device.(6) There must, he says, be some actuality that is prior to substantial form that allows for the divisibility of terrestrial bodies and the variability of their specific dimensions. This form is neither a substantial nor an accidental form, and it is not matter. It is common to all corporeal substances on this earth.

Let us contrast this now with what Albert says about the heavenly bodies. To start with, the substantial form of the heavenly body is not the form of a body. The Intellect or Intelligence that serves as the form of the heavenly body is not united to the heavenly body as the form that is the act of a body. As eternal movers and as fully actual knowers, the heavenly Intellects or Intelligences have, in certain areas, unlimited powers, such that these very powerful beings cannot be strictly bodily forms. They are called "substantial forms," but they are not united to their bodies as form is united to matter.(7) Rather, they serve as substantial forms as mover is united to thing moved. And this implies something else. The matter, of which these Intelligences are the substantial forms, does not require a mediating form of corporeity, for the very reason that the substantial form in this case is not a bodily substantial form. This, in turn, implies that the matter of the heavenly bodies is not divisible, for matter of itself is not divisible. But if the matter of the heavenly bodies is not divisible, then the heavenly body is not liable to contrary qualities, which require divided parts; and if the heavenly body is not liable to contrary qualities, then it is not liable to destruction. Thus, the heavenly body is incorruptible because the matter of the heavenly bodies, lacking the forma corporeitatis, has no capability of receiving contrary qualities. Again, let me quote Albert.

The following is Aristotle's opinion, from what can be inferred from his words, for he has never given his opinion explicitly in any of the works that have come into my knowledge. The Intelligence is the form of the heavenly body, and the matter of the heavenly body is capable of receiving such a form before receiving corporeity. For this reason, Aristotle frequently says that there is not one matter of the heavens and of corruptible bodies. Now, the heavens do have the corporeity of determinate dimensions and shape, but this does not come from these dimensions being brought from the potency of matter, as such potency would be a potency of indeterminate dimensions for receiving the form of a body. Rather, because the motion of the heavens is a bodily motion and because the Intelligences are the movers, the heavenly bodies have the requisite determinate dimensions, but they do not receive their substantial forms through the mediation of corporeity. This is the reason why intellectual substances are indivisible and immobile, for the divisibility and mobility is in their bodies, not in them. Because they are not divisible by reason of bodily divisibility, Aristotle determined that such forms are not brought into being through a material subject, as bodily forms are brought into being from the potency of matter. Rather, all of these forms are brought into being, in their proper celestial ranks and orders, by the First Cause. Hence, Aristotle has said that the separate substances and the human intellect for one and the same reason must be brought into being by an extrinsic cause [and not from the potency of matter] . . .(8)

There are three features of Albert's position that are particularly noteworthy, and all three will become important when we consider Thomas' position. First, we should take note of the fact that Albert adopts a dualist solution to the problem of the heavenly bodies. The Intelligences are the substantial forms of the stars and the planets but they are not the acts of the celestial bodies. In some way, the heavenly bodies, before being moved by their Intelligences, are already constituted as complete subjects that can be moved by the Intelligences. The creator, presumably, creates both the heavenly bodies and their movers, and he unites them, not as matter and form, but as thing moved and mover. There is, however, precedence for this dualism: the heavenly bodies are united to the Intelligences in the same way as the human body is united to the human soul. Albert in the text quoted compares the human to the celestial intelligence; he goes on to say that the position he attributes to Aristotle is also that of Averroes.(9) I have argued elsewhere that there is a dualism in Albert's account of man.(10) Like Averroes, Albert makes the heavenly body something separate from its intellectual substantial form.

Second, Albert is attributing the incorruptibility of the heavenly bodies to a basic feature of matter itself: matter, prime matter, is in itself indivisible; as indivisible, matter is not liable to contrary qualities. The matter of terrestrial bodies, by contrast, is inherently divisible, because such matter always possesses a "form of corporeity" by which it is divisible. From its inherent divisibility comes the inherent corruptibility of the earthly bodies. In effect, then, Albert has presented us with a doctrine of two types of prime matter; there is the prime matter of the heavens, which lacks an inherent forma corporeitatis, and the prime matter of the earth, which has an inherent forma corporeitatis. Prime matter is, of course, absolutely without form, and yet some prime matter has an inherent corporeity and some does not.

Third, in the text we have seen above, Albert has said that in some sense the power of the celestial Intelligences is unlimited.(11) As a being with unlimited power, it cannot be a bodily form, for bodily forms are always limited to finite bodily operations. In another text, his contemporaneous paraphrase of the Physics, Albert draws out another consequence of the unlimited power of the Intelligences.(12) He points out that the potency of the heavenly body is different from the potency of the earthly bodies. Following Aristotle, Albert says that the heavenly body has a potency for place only, but that the earthly bodies have a potency for place and generally for form. In the case of the heavenly bodies, Albert says that the matter of these bodies is "completely taken up" by the substantial form. As it were, the infinite power of the celestial Intelligences satisfies the inherent potency of prime matter for form. But for the infinite power of the Intelligences, the potency of prime matter would not be satisfied and would be in potency not only for place but also for some other substantial form.

We shall meet with these three features of Albert's position when we look at Thomas' account. Thomas, by my count, has given three different answers to the problem of how it is that the heavenly bodies are incorruptible. All of these answers owe something to Albert, but the specifically Averroistic note of Albert's position is, although early attractive to Thomas, finally rejected by him.

Before we turn to Thomas Aquinas, it might be helpful to say just a word about Averroes. In his Commentary on the Physics, from which Albert drew heavily, Averroes' position on the heavenly bodies seems to be this.(13) Prime matter necessarily means a potency for substantial change. Further, Averroes recognizes that any composed material being can only be a composite of prime matter and substantial form. It follows from this that if we deny that there is any potency for substantial change in the heavenly bodies we must also deny that the heavenly bodies are composite bodies. This seems to be one of the key Averroistic points that Albert adopted. The heavenly bodies will have to be material bodies but also simple, non-composite bodies. From this, two things seem to follow. On the one hand, the heavenly bodies will be numerically one and actual just in and of themselves. They do not require a bodily form to make them actual, for they are simple beings, ex hypothesi. On the other hand, they are purely inert, neutral lumps of matter that cannot perform any operations of their own. They do, therefore, require a mover to actualize them into motion. In this sense, the Intelligences, which are the movers of the heavenly bodies, are both separate (not the forms of the heavenly bodies) and also in some sense the substantial forms of the bodies. Such is the position of Averroes, which, I believe, is also largely that of Albert.

Early in his academic career, when commenting on the Sentences of Peter Lombard, Thomas clearly opts for the position of Averroes and Albert.(14) The essence of this position, as Thomas gives it, is that the heavenly bodies are not composed bodies. The heavenly bodies simply are complete subjects in themselves; their matter is not the prime matter of earthly things. Rather, the bodies of the planets and stars simply are made by the Creator to be complete material subjects.(15) These complete subjects, of course, require movers, and the separate Intelligences provide this function. Prime matter, by contrast, is in itself a potency to all forms, and yet it can only exist at any one time under one substantial form. Any time matter exists it will be both actually existing under one substantial form and also in potency toward some other form or forms. But whenever there is a potency toward some form, says Thomas, there must be an active power that can bring that potency into actuality, for otherwise the potency would exist in vain. If we suppose that the heavenly, incorruptible body is matter existing under one substantial form but in potency toward other forms, then we must either suppose that there is some active potency that could bring the potency into actuality, or we must suppose that the potency exists without any active means of actualizing it. The first possibility, however, would amount to admitting that the incorruptible bodies really are corruptible, for if some active power is able to make them lose their substantial form and acquire another, then by that fact they are corruptible bodies. We know, however, that the heavenly bodies are incorruptible. On the other hand, the second possibility amounts to the claim that there exists a potency that is in vain, but nature does nothing in vain, and hence such a purposeless potency would be unnatural. Therefore, concludes Thomas, we cannot claim that the heavenly bodies are composed of form and matter.

This position, of course, will later seem to Thomas to be defective. If a substance is simple, not composed, Thomas will later point out, it can only by a subsistent or separate form. If a substance is material (and as the heavenly bodies are clearly visible, they are surely material) it must be something other than a pure form. The heavenly bodies, since they are material, must be composed of form and matter. Some other solution, therefore, must be found to the problem of explaining the natural incorruptibility of the heavenly bodies.

A second position that can be found in Thomas' writings is the position that, although the heavenly bodies are indeed composed of matter and form, the prime matter of which the heavenly bodies is composed is not the same sort of prime matter of which the terrestrial bodies are composed.(16) Prime matter has in itself no form or actuality. Prime matter insofar as it is the substrate of generable and corruptible beings is in potency to any form that can be generated. This means that such prime matter has a sort of universal potentiality: it can be realized in an indefinite number of different substantial forms. The prime matter of the heavenly bodies is radically different, however. It can only be realized in one substantial form. Whereas the potency of earthly prime matter is a universal potentiality for any form, the potency of heavenly prime matter is a potentiality for one form only. Since matter is defined as potentiality, and since the potentialities of the heavenly and the earthly matters are so radically different, it follows that there are two types of prime matter.

This solution is widely taken by scholars to be Thomas' fundamental solution to the problem of the incorruptibility of the heavenly bodies.(17) I find this perplexing, however, for two reasons. First, philosophically, I cannot see how this position is tenable. Matter is potency; the principle of all actuality is form, not matter. To talk about kinds or types of prime matter is to accord some sort of actuality or form to prime matter. The very notion of the pure potency of prime matter is incompatible with any notion of kinds or types of prime matter. As soon as we have specified matter in some way, as soon as we talk about a potency for this or for that specific form, we are talking no longer about prime matter but about some sort of secondary matter. We are talking about matter that is informed matter. If it is true that the matter of the heavenly bodies is in potency to only one substantial form, then such a restriction of prime matter can only come about because of form. Matter can only be a certain kind of matter because of form. But then we are talking about secondary, not primary, matter.

Second, Thomas never quite, even in the texts that support this interpretation, uses the language that he is supposed to use. He never says that there are two types or kinds of prime matter. He often says that the matter of the heavenly bodies is different from the matter of the earthly bodies, or he will say that the matter of heavenly and earthly bodies is only one by analogy. But speaking in this way does not necessarily commit Thomas to the tenet that there are two kinds of prime matter. When Thomas says that the matter of the heavenly bodies is different from the earthly, he can be taken to mean that the secondary matter is different. Or when he says that the matter of the heavens and the earth is only one matter by analogy, he could simply mean that the ether of the heavens is only analogously like the elements here on earth. To my knowledge, Thomas never explicitly says what he ought to say if he really did hold that there are two kinds of prime matter.(18)

For this reason, then, we find in Thomas also a third explanation of the incorruptibility of the heavenly bodies.(19) In what I take to be his most magisterial arguments on this problem, Thomas affirms that the heavenly bodies are composed of prime matter and of substantial form but that it is by reason of the form, not the matter, that the heavenly body is incorruptible. Prime matter does indeed have a universal potency, but this universal potency can be fully satisfied by a form that is sufficiently noble or eminent to satisfy the entire potency of prime matter. This would mean, of course, that the forms of the heavenly bodies are of a very different sort from the forms of earthly bodies. Whereas the form of any terrestrial body is essentially a finite sort of actualizer, such that it can actualize matter to be just this but cannot remove from matter the basic potency for some other form, the form of the heavenly body, by contrast, exerts a kind of infinite power over prime matter such that there is no privation to be found in the heavenly body. On this account, there are not two types of prime matter, for prime matter is undifferentiatedly one. Rather, the forms of the heavenly bodies completely satisfy the potency of prime matter in a way that the forms of earthly bodies do not.

This is, in my judgment, Thomas' most successful solution to the problem, but it is still in the end an unsuccessful solution. The difficulty with this position, as Albert realized, and as Thomas himself realized at least once, is that the potency of prime matter is really infinite. There is no limit to the number of forms to which prime matter is in potency. To suppose, therefore, that some form could satisfy the whole of such a potency is to suppose that there is a form of infinite power. The Intelligences, of course, are infinitely able to move the heavenly bodies, but they are not, by that reason, infinite in power.

All three of Thomas' attempted solutions are based upon features of Albert's position. The notions that the heavenly bodies are not composed bodies, that there are two types of prime matter, and that the form of the heavenly body has an unlimited power can all be found in Albert's teaching. Yet, in the end, Albert's position rests upon two Averroistic notions that the mature Thomas came to reject. For one, Thomas rejected the idea that there could be a body that was not composed of form and mater. For another, Thomas rejected the notion that there could be some form, like the forma corporeitatis, that was neither substantial nor accidental. These are both Averroistic tenets that Thomas came to reject, although it must be said that Thomas himself did not have an adequate solution to the problem and that each of his three attempted solutions were heavily indebted to Albert.

The second major problem I wish to examine is that of explaining how elements remain in compounds. The problem is that when an element becomes a part of something else the element is supposed to remain in that of which it becomes a part. And yet the element cannot remain as a substance, for the elements undergo a substantial change when they become part of a compound. According to ancient and mediaeval chemistry, there are four elements (fire, air, water, and earth), and these elements can become part of a living organism, for example. When fire becomes part of a living animal, in some way the fire is in the animal, but it is not simply present as the substance fire, for if it were the animal would, presumably, be burning. The problem, then, is to explain how it is that elements, when they become parts of compounds, undergo substantial change and yet do remain as elements in the compounds.

Albert recognizes the full force of this problem. On the one hand, Albert always insists, as does Thomas, that there can only be one substantial form for any one substance.(20) A plurality of substantial forms, says Albert, results in the absurdity that a substance is simultaneously in more than one substantial category; or it results in the absurdity that a substance is not one thing but is really many things. On the other hand, Albert is well aware that there is a fundamental difference between any substance that is a compound of elements and a substance that is but one simple element.(21) The compound always manifests a plurality of qualities that attest to the presence of more than one element. Futhermore, the fact that compounds decompose, not randomly into just any elements, but always regularly into certain, predictable elements indicates that elements really are in some way in the compounds.(22)

To solve this problem, then, Albert stipulates two things. First, the presence of elemental properties in compounds can only be caused by the substantial form of the elements.(23) Since the properties of elements naturally arise only from the substantial form of the element, it seems to follow that the elemental substantial form must be really present whenever the elemental properties are present.

Second, Albert would recognize a distinction between the first and second being of the elements.(24) The first being of the elements is that which is associated with or identified with the form of the element. This first being remains in the compound in which the element is found, but it remains in the compound in a confused or indistinct way. Hence, the form of the element is present in the compound, but the existence or being that this elemental form has is not the distinct or determinate existence that substantial forms have in the natural substances of ordinary experience. The secondary being, however, is the being associated with or identified with the proper accidents of the element, that is, the various powers or tendencies that the element naturally has. This second being should be understood as the exact degree or intensity of the elemental powers. Fire, for example, on the ancient theory has the tendency to be hot, and fire in its pure state has an exact degree or intensity of heat. In a compound such as an animal, there is also heat, and hence, fire. But there is not in the animal the exact intensity of heat that is found in fire, for the animal is not as hot as is pure fire. According to Albert, the primary being of fire - fire in some degree - is present in the animal, but the secondary being of fire - the exact degree of pure fire - is not present in the animal. The being of the animal's substantial form is present in the animal, and the being (primary) of the elements is present, but the secondary being of the elements is not present.

This position, Albert reports, is also the position of both Avicenna and Averroes, who, in spite of some verbal differences, agree that the substantial forms of the elements are actually present in compounds.(25) They both affirm that the substantial form of the compound is the result of the mixing of the elements out of which the compound is made. This mixing results in a new form which is something distinct, but its components really do remain, although they remain as indistinct formal realities.

What makes this possible is Albert's conviction that the form of the element is not a substantial form in the sense in which something perfect and complete in nature has a substantial form.(26) A substantial form that is the form of something perfect in nature, like the form of a living organism, cannot be intensified or diminished, for there cannot be more or less of such a form. The form of an element, however, is the form of something that is incomplete and imperfect. The element, says Albert, is not really a substantial thing in its own right, for it is fundamentally a via ad aliud(27). It is a constituent that accounts for the reality of other substances, but it is not really a substance all on its own. And yet, elements are substances and not accidents. Albert recognizes the fact that, on the mediaeval account, the elements seldom or never exist on their own in their pure state. The earth we walk on, the water we drink, the air we breathe, and the fire we burn are all already compounds. Each is predominantly composed of its most obvious element, but each one is also composed of the other elements.(28) Albert, therefore, is driven to the conclusion that the form of the element is a sort of intermediate form. It is not an accidental form or a substantial form; it is not completely indeterminate like prime matter, but it is not completely determinate like a real substantial form. Hence, between accident and substance, between prime matter and substantial form, there is a kind of intermediate form, the form of an element.

When Thomas Aquinas confronts the same problem, he is initially attracted to Albert's position. Using the distinction between first and second being, Thomas will agree that it is possible to explain how the elements can remain in a compound.(29) The elements remain in the compound in that the first being of the substantial forms of the elements remains, but the full substantial, or secondary being, does not remain in the compound. This position, which Thomas attributes to Avicenna, is Albert's position; Thomas adopts it in his Commentary on the Sentences of Peter Lombard.

In his maturity, however, Thomas rejects the position of both Avicenna and of Averroes, and in doing so also rejects the position of his teacher Albert. In refuting the position attributed to Avicenna, Thomas rejects part of Albert's position. Avicenna holds that in some way the substantial forms of the elements must remain actually in the compound. Fundamentally, the difficulty with Avicenna's position is that is implies that the elements are not really part of a compound but only apparently part of a compound.(30) What is apparently a new compound (a mixtio) is really just a collection of independent substances into one place. Such a mere apparent compound would not take on genuinely new properties, as any true substance should.

The position of Averroes, on the other hand, attempts to avoid having to posit a mere apparent compound (mixtio ad sensum), but it does so at the cost of advancing what Thomas calls a ridiculous position. Averroes holds that the forms of the elements are neither true substantial forms nor true accidental forms but that, being close to prime matter, they are an imperfect sort of form.(31) They bear a resemblance to the accidental form precisely in this, that they can be "more" or "less". That the forms of the elements can be more or less means that they can be mixed together in a compound without compromising the substantial unity that comes from the substantial form. They are, so to speak, substantial forms that behave like accidental forms when they are in a compound. And this, of course, is very much like the view of Albert, that the forms of elements are a sort of hybrid form between the substantial and the accidental.

According to Thomas, however, it is impossible that there be some sort of form that is in between the substantial and the accidental form, just as it is impossible that there be something between an affirmation and its denial.(32) A substance is defined as that which does not inhere in another as in a subject, whereas an accident is defined as that which does inhere in another as in a subject. A subject in this context means a hoc aliquid, a substance. Either something does inhere in a substance, and if so it is an accident, or it does not inhere in a substance, in which case it is a substance. There is no third possibility, nor can there be.

The combined arguments against Avicenna and Averroes amount to arguments against Albert. In rejecting Avicenna, Thomas is rejecting Albert's contention that the substantial form of the element must be present to account for the presence of elemental qualities. In rejecting Averroes, Thomas is rejecting Albert's position that the elemental substantial form is a sort of hybrid form between the substantial and accidental form.

Thomas' own position is that the elements remain in a compound, not insofar as the substantial forms of the elements remain, but only insofar as the active and passive qualities of the elements remain.(33) These active and passive qualities remain in the states that are more or less; that is, the precise amount of the qualities that are in the compound will be different from the amount of the quality that can be found in the pure element or that can be found in another compound. The warmth that is in mammals is from the element fire, for example, but the precise amount of warmth that is appropriate to a mammal is different from the amount of heat that is in pure fire and different again from the amount of warmth in a plant. That there is warmth in the mammal is caused by the presence of the element fire; that it is just the right amount is caused by the substantial form of the mammal. The elemental powers thus remain in the compounds and become the powers of the compound. The elements themselves, says Thomas are present in the compounds in virtute, which means that the substantial forms of the elements are not present but that the elemental qualities are present, but present precisely as determined by the substantial form of the compound.

We have seen how Albert and Thomas treat two important problems concerning matter. In each case, we have seen that Thomas reflects the doctrine of his teacher, but we have also seen that Thomas has come to reject certain tendencies in Albert that can be associated with Averroes. In common between Albert and Thomas are at least two fundamental doctrines. First, both Dominicans recognize the pure potentiality of prime matter. Matter in its most fundamental sense is a potency for form. This potency is not of itself determined in any way; determinations of matter come entirely from form. Second, both Albert and Thomas hold, against most if not all of their contemporaries, that there is but one substantial form for any one substance. On the other hand, in explaining both the heavenly bodies and the presence of elements in a compound, Albert manifests certain Averroist tendencies that Thomas comes to reject. The manifestation of this Averroism is, I think, the tendency in Albert to recognize some sort of form that is neither substantial nor accidental. In the case of the heavenly bodies, Albert needs some form whereby he can distinguish the prime matter of the heavens from the prime matter of this earth. This form is the forma corporeitatis, the form that is present in all earthly matter and absent in all celestial matter. In the case of elements present in a compound, Albert requires a transitory form that is not quite a full substantial form nor yet an accidental form, for Albert wishes to say that the element both is and is not substantially present in a compound. For this, he needs a form that both is and is not a substantial form. In both of these cases it is this tendency to try to find a third sort of hybrid form that Thomas rejects in his mature doctrine. There cannot be, Thomas recognizes, any form that is prior to substantial form or that falls in between substantial and accidental form.

Although Thomas does reject Albert's position on each of these topics, it must be remembered that the principal lines of Thomas' position are already to be found in Albert. Thomas may have found his way more clearly and farther than did Albert, but he could only have done so because Albert went so far and so well before him.


1. Printed version: "St. Albert the Great and St. Thomas Aquinas on the Presence of Elements in Compounds," Sapientia 54 (1999) 41-57.

2. I would also like to note that both of these problems are very important for maintaining the entire project of Thomistic natural philosophy. Their importance lies in their connection to the cosmology with which Thomas worked. It is often supposed, wrongly, that Thomistic natural philosophy is connected to an outmoded, thirteenth-century cosmology such that, as we now reject the cosmology so we now must also reject the philosophy. I would argue, however, that on both the question of the heavenly bodies and on the question of the presence of elements in a compound Thomas' natural philosophy transcends his cosmology. I have made these arguments in the article cited in note # 1 and in a paper entitled "What Thomas Aquinas Should Have Said About the Heavens", American Catholic Philosophical Association Annual Meeting, November, 1999.

3. "Dicimus igitur notum esse ex his quae determinata sunt in primo Physicorum, materiam primam esse substantiam in potentia existentem et nullam omnino formam habentem in actu; sed est simplex substantia in potentia existens. Quod si esset simplex substantia in actu existens, esset ipsa forma, et cum forma non sit receptibilis formae, non posset materia prima recipere formam aliquam. Per privationem autem, quae est in ipsa, subicitur mutationi, quae est via ad formam, et efficitur potentia recipiens formam. Et ideo potentia est quasi differentia substantialis in ipsa, quae distinguit eam et a forma et a composito, quia si haberet formam quemadmodum compositum, tunc absque dubio non esset receptibilis alicuius formae, quamdiu haberet illam, eo quod secundum intellectum nullum verum sit unum numero subiectum duas simul habere formas substantiales. Et ideo in Physicis dictum est, quod non intelligibilis est materia nisi per analogiam ad formam et non per formam aliquam quam habeat." De caelo 1.3.4 (Cologne 5,1; 62.15-34).

4. "Est autem duplex forma substantialis, quarum una est divisibilis et quasi dimensa et finita divisione et dimensione et finitione materiae et illa proculdubio actus et perfectio corporis est, habens virtutem in corpore, sicut diximus in octavo Physicorum. Altera autem nec divisibilis est nec dimensa nec finita per materiam et haec non est actus alicuius corporis nec perfectio ipsius, sicut est forma, quae dicitur intelligentia sive intellectus." De caelo 1.3.4 (Cologne 5,1; 62.43-50).

5. "Cum autem materia non dividatur ita, quod per partes subiaciatur diversis formis nisi per quantitatem, eo quod secundum se indivisibilis est, sicut ostendimus in primo Physicorum, oportet, quod materia, quae suscipit formas, quae sunt actus et perfectiones corporis, sit primo susceptibilis trium dimensionum, non tamen terminatarum ad certam dimensionem, quia si certae dimensiones essent materiae, contingeret, quod continue corrumperentur in omni generatione et corruptione; et hoc non esse verum ostendimus in primo Physicorum. Propter quod suscipit primo formam, quae est corporeitas indeterminatarum dimensionum, qua mediante divisibilis efficitur et diversis formis substantialibus per partes subicibilis Et haec corporeitas est communis omnibus formis, quas suscipit, quia, sicut ostendi habet in secundo Peri geneseos, forma communis in materia omnibus vel pluribus substantiis non mutatur, quando mutantur formae substantiales. Sicut patet, quando mutatur ignis in aerem, remanent caliditas et diaphanitas eaedem in essentia, licit habeant diversum esse in igne et in aere, et ita corporeitas materiae, quae est sicut forma prima respectu omnium formarum, quae sunt perfectiones corporeae, remanet in ipsa, et numquam dedudatur ab ipsa in aliqua transmutatione quorumcumque corporum; et si denudaretur, contingeret, quod corpus esset ex omnino non-corpore et quod fieret corpus ex nihilo omnino, et hoc ostendimus impossibile esse secundum naturam in primo Physicorum." De caelo 1.3.4 (Cologne 5,1; 62.59-63.2)

6. Averroes, De substantia orbis, cap. 1 (f. 320B-E).

7. De caelo 1.1.3 (Cologne 5,1; 10.26-48); De caelo 2.1.5 (Cologne 5,1; 115.5-24).

8. "Et illa [sententia] quidem quae est Aristotelis, sicut conici potest ex verbis suis, licet in nullo loco expresse dicat in libris, quorum notitia ad nos pervenit, est, quod intelligentia sit forma caeli et quod caeli materia sit susceptibilis huiusmodi formae ante corporeitatem. Propter quod Aristoteles frequenter dicit, quod non est una materia caeli et corporum generabilium et corruptibilium. Et quod caelum habet corporeitatem determinatarum dimensionum et rotundarum superficierum, hoc non est ideo, quod istae dimensiones eductae sint de potentia materiae, quae potentia est dimensionis indeterminatae, qua recipit formas corporis, sed potius, quia motus caeli non est nisi corporis. Et quia intelligentiae sunt moventes, oportuit caelum habere determinatas dimensiones, cum tamen substantiales formas suas primas mediante corporeitate non recipiant. Et haec est causa, quare substantiae intellectuales sunt impartibiles et immobiles per se, quia non movetur nisi corpus et non dividitur nisi quantum vel quod est in quanto sicut in subiecto. Et quia sunt indivisibiles divisione subiecti, ideo determinavit Aristoteles, quod tales formae sunt non constitutae per subiectum sive per materiam, quemadmodum corporum formae omnes per materiam consituuntur quoad hoc quod educuntur de materia sicut actus de potentia. Sed potius omnes istae sunt constitutae a causa prima secundum omnes ordines caelorum et caelestium corporum. Et ideo dixit Aristoteles eas esse substantias separatas et hac eadem de causa dixit intellectum hominis ingredi ab extrinseco, quia omnis forma educta de potentia ad actum secundum potestatem materiae educitur et non potest esse nisi limitatae operationis, quia cum materia efficitur actu, tunc dividitur et non dividitur nisi per corporeitatem, ut diximus, et ideo omnis forma educta de materia sicut de potentia, est consequens corporeitatem. Dico autem consequens natura, non tempore." De caelo 1.3.4 (Cologne 5,1; 63.63-64.8).

9. "Haec est ergo probatio subtilissima, quam intendit Aristoteles in primo Caeli et mundi. Et in hanc sententiam omnimodo convenit Averroes, sicut apparet legenti primum librum eius, quem De substantia orbis intitulavit." De caelo 1.3.4 (Cologne 5,1; 64.77-81).

10. "St. Albert the Great on the Union of the Human Soul and Body," American Catholic Philosophical Quarterly 70 (1996) 103-120.

11. "Forma autem, quae est intellectus, sicut per se apparet et in Prima Philosophia probatur et in libro De anima, est universaliter agens et universaliter quodammodo patiens. Agit enim universaliter omnes formas et est quodammodo omnia potentia possibilis intellectus. Et quia sic non limitatae est operationis, impossibile est, quod ipse sit forma corporis recepta mediante corporeitate, quia, sicut ostemdimus, omnis actus corporis limitatas habet operationes." De caelo 1.3.4 (Cologne 5,1; 63.45-53).

12. "Et horum [scil. corporum motorum] est materia una prima, quae tamen dividitur secundum primam potentiae divisionen, quae est potentia ad ubi tantum et potentia ad formam. Et quia istae potentiae divisae sunt secundum esse et per proximas materias, eo quod in his in quibus potentia est ad ubi tantum, est tota materia eorum, quae susceptibilis est formae talium corporum, in his autem in quibus est potentia ad ubi et ad formam, non est tota materia susceptibilis illius formae intra ea, ideo aequivoca est materia in illis, si ratio materiae sumatur secundum esse physicum, quod habet in corporibus illis." Physica 1.3.11 (Cologne 4,1; 60.2-12).

13. Averroes, De caelo, lib. 1, t.c. 95 (Venice 5; f. 63K-64F); lib. 1, t.c. 20 (Venice 5; f. 15C-D).

14. "Avicenna enim Suff., lib. I, cap. iii, videtur ponere unam materiam esse omnium corporum, argumentum ex ratione corporeitatis assumens, quae cum sit unius rationis, una sibi materia debetur. Hanc autem positionem Commentator improbare intendit in princ. Caeli et mundi et in pluribus aliis locis, ex eo quod cum materia, quantum in se est, sit in potentia ad omnes formas, nec possit esse sub pluribus simul, oportet quod secundum quod est sub una inveniatur in potentia ad alias. Nulla autem potentia passiva invenitur in natura cui non respondeat aliqua potentia activa, potens eam in actu reducere; alias talis potentia frustra esset. Unde cum non inveniatur aliqua potentia naturalis activa quae substantiam caeli in actum alterius formae reducat, quia non habet contrarium, sicut motus ostendit, quia motui naturali eius scilicet circulari, non est aliquid contrarium ut dicitur in I Caeli et mundi, text. 20, oportet quod in ipso nihil inveniatur de materia prima inferiorum corporum. Nec potest dici, quod materiae prout est sub forma caeli, tota potentia terminetur, ita quod nihil remaneat in eadem potentia ad aliam formam; non enim terminatur potentia nisi per adeptionem formae, ad quam erat in potentia; unde, cum materia prima secundum se considerata sit in potentia ad omnes formas naturales, non poterit tota ejus potentia terminari nisi per adeptionem omnium formarum. Non enim una forma recepta in materia, etiam si sit nobilior et magis perfecta, tollit potentiam ad formam aliam minus nobilem; materia enim sub forma ignis existens, adhuc remanet in potentia ad formam terrae. Unde etsi forma caeli sit nobilissima, nihilominus tamen, recepta in materia prima, non terminabit totam potentiam ejus, nisi simul cum ipsa recipiantur omnes aliae formae; quod est impossible. Et praeterea si poneretur quod forma caeli per suam perfectionem, totam materiae potentiam terminaret, adhuc oporteret quod materia stans sub forma elementari, esset in potentia ad formam caeli, er reduceretur in actum per actionem virtutis caslestis; et ita caelum esset generabile et corruptible. Et ideo ipse vult quod nullo modo in materia conveniant superiora et inferiora corpora: et hoc videtur probabilius, et magis consonum dictis Philosophi, XII Metaph., text. 10. Nec dico, sicut quidam dicunt, quod conveniunt in materia, si sumatur pro fundamento primo, quod nec est album nec est nigrum, ut dicitur in I Metaph. Text. 16, sed differunt in materia secundum quod materia determinatur per motum: diversitas enim motus est signum diversitatis materiae, et non causa, sed e converso: quia motus est actus existentis in potentia; unde oportet quod ubi invenitur una materia per essentiam; inveniatur potentia respectu ejusdem motus, secundum quod materia est in potentia ad plura." Commentum in librum 2 Sententiarum, d. 12, q. 1, a. 1, sol. (Mandonnet-Moos 2; 302-303).

15. "Ad quintum dicendum, quod, sicut in I De gen., cap. III, dicitur, materia est immediate subjectum generationis et corruptionis; aliorum autem motuum per prius et posterius, tanto plus quanto illud secundum quod est mutatio, majorem perfectionem motus praesupponit: et ideo in illis tantum est unitas materiae primae quae in generatione et corruptione conveniunt, et per consequens etiam illa quae conveniunt in tribus motibus, scilicet augmento, et diminutione, et alteratione, secundum quod augmentum et diminutio non est sine generatione et corruptione, quae etiam alterationis terminus est. Sed loci mutatio, ut in VIII Physicor. probatur, est maxime perfecta, quia nihil variat de eo quod est intraneum rei; unde subjectum hujus motus est ens completum in esse primo, et in omnibus proprietatibus intraneis rei; et talis motus convenit corpori caelesti; et ideo materia ejus est sicut subjectum completum in istis inferioribus, ut dicit Commentator in lib. De substantia orbis; unde remanet communitas materiae secundum analogiam tantum." Commentum in librum 2 Sententiarum, d. 12, q. 1, a. 1, ad 5 (Mandonnet-Moos 2; 304).

16. "Supposito autem quod nulla forma quae sit in corpore corruptibili, remaneat ut substrata generationi et corruptioni, sequitur de necessitate quod non sit eadem materia corporum corruptibilium et incorruptibilium. Materia enim, secundum id quod est, est in potentia ad formam. Oportet ergo quod materia, secundum se considerata, sit in potentia ad formam omnium illorum quorum est materia communis. Per unam autem formam non fit in actu nisi quantum ad illam formam. Remanet ergo in potentia quantum ad omnes alias formas. - Nec hoc excluditur, si una illarum formarum sit perfectior et continens in se virtute alias. Quia potentia, quantum est de se, indifferenter se habet ad perfectum et imperfectum; unde sicut quando est sub forma imperfecta, est in potentia ad formam perfectam, ita e converso. - Sic ergo materia, secundum quod est sub forma incorruptibilis corporis, erit adhuc in potentia ad formam corruptibilis corporis. Et cum non habeat eam in acu, erit simul sub forma et privatione; quia carentia formae in eo quod est in potentia ad formam, est privatio. Haec autem dispositio est corruptibilis corporis. Impossibile ergo est quod corporis corruptibilis et incorruptibilis per naturam sit una materia." Summa theologiae 1.66.2 (Ottawa, 403a-404b).

17. Thomas Litt, Les corps célestes dans l'universe de saint Thomas d'Aquin (Louvain-Paris: Publications Universitaires, 1963) 54-90. Litt, however, does find one text, Thomas' Commentary on the De Trinitate of Boethius (lect. 2, q. 1, a. 4, ad 4), in which Thomas denies that there are two kinds of prime matter, but Litt simply records this as an aberration from Thomas' otherwise consistent position (pp. 86-90). John Wipple, The Metaphysical Thought of Godfrey of Fontaines, (Washington: The Catholic University of America Press, 1981) pp. 285-291, recognizes that Thomas did hold at times an Averroist position, but Wipple concurs with Litt that Thomas' mature position is that there are two types of prime matter. See also Joseph Bobik, Aquinas on Matter and Form and the Elements (Notre Dame, IN: The University of Notre Dame Press, 1998) pp. 185-186. Bobik holds that, for Thomas, there simply is no prime matter in the heavenly bodies, whereas the sublunary elements all do have prime matter. Later, however, Bobik points out that Thomas makes the incorruptibility a function of the substantial form of the heavenly body which so perfect the body as to remove all potency for other substantial forms (pp. 199-202). This later comment accords more closely with what I take to be the mature position of Thomas.

18. Yet I will concede that Thomas at least in some texts, such as Summa theologiae 1.66.2, does seem to hold this position, for Thomas gives the relevant argument that would seem to support this position.

19. "Oportet ergo in corpore caelesti ponere aliquod subiectum suae actualitati. Non tamen oportet quod istud subiectum vel materia habeat privationem: quia privatio nihil aliud est quam absentia formae quae est nata inesse, huic autem materiae vel subiecto non est nata inesse alia forma, sed forma sua replet totam potentialitatem materiae, cum sit quaedam totalis et universalis perfectio. Quod patet ex hoc, quod virtus activa eius est universalis, non particularis sicut virtus inferiorum corporum; quorum formae, tanquam particulares existentes, non possunt replere totam potentialitatem materiae; unde simul cum una forma remanet in materia privatio formae alterius, quae est apta nata inesse. Sicut etiam videmus quod corpora inferiora sunt susceptiva diversarum figurarum: sed corpus caeli non est figurabile alia figura. Sic igitur in corpore caelesti non est privatio alicuius formae, sed solum privatio alicuius ubi. Unde non est mutabile secundum formam per generationem et corruptionem; sed solum secundum ubi. Ex quo patet quod materia caelestis corporis est alia et alterius rationis a materia inferiorum corporum, non quidem per aliquam compositionem, sicut Philoponus existimavit; sed per habitudinem ad diversas formas, quarum una est totalis et alia prtialis: sic enim potentiae diversificantur secundum diversitatem actuum ad quos sunt." De caelo lib. 1, lect. 6, 63. See also De substantiis separatis cap. 8, 86.

20. "Adhuc autem, videbitur forte alicui quaerendum de formis substantialibus elementorum, utrum maneant in commixto ex elementis vel non. Si enim manere dicantur, tunc videbitur consequi necessario, quod compositum plures habeat formas substantiales, et ad hoc multa sequuntur inconvenientia, quorum unum et primus est, quia nihil simul suscipit multas formas substantiales, ergo nec compositum; adhuc autem, quia per multas formas substantiales poneretur in diversis speciebus; adhuc autem, quia non esset vere unum, sed potius esset contiguum vel per accidens unum, quae omnia absurda sunt." De caelo 3.2.8 (Cologne 5,1; 240.56-68).

21. "Si autem [formae substantiales elementorum] non manent, tunc videtur, quod cum materia mixti nullam habeat actu formam, nec simplicis videlicet neque compositi, quod privatio ipsius est adeo generalis sicut privatio materiae primae; sed prima materia est simplex, ergo et materia compositi, quod omnino est absurdum; adhuc autem secundum hoc materia communis et prima per nihil efficeretur propria huius vel illius materia." De caelo 3.2.8 (Cologne 5,1; 240.68-75).

22. De caelo 3.2.8 (Cologne 5,1; 240.96-241.4).

23. "Cum igitur sciamus proprietatem nusquam esse sine proprio subiecto, oportebit, quod secundum aliquem modum elementum infit composito secundum formam substantialem." De caelo 3.2.8 (Cologne 5,1; 240.93-96).

24. "Si autem haec omnia forte aliquis vellet solvere dicens, quod elementa manent secundum medietates suarum formarum et secundum medietates alterantur ad invicem, sicut videtur dicere Aristoteles in fine primi Peri Geneseos, videtur hoc esse inconveniens, eo quod formae substantiales non recipiunt intensionem er remissionem, et sic non possunt intendi et remitti." De caelo 3.2.8 (Cologne 5,1; 241.5-14).

25. De caelo 3.2.8 (Cologne 5,1; 241.39-59).

26. "Iam enim patet, qualiter materia compositi differt a materia prima, et qualiter unius et eiusdem non sunt plures formae, prout forma est finis et perfectio ultima, distincta secundum esse. Hoc enim solo modo intelligitur, quod unius et eiusdem non sunt formae multae, quia formae confusae et indistinctae sunt in materia, sicut potentia propria ad formam ultimam. Hoc autem quod dicitur, quod formae substantiales non intenduntur et remittuntur, est aliquo modo verum et aliquo modo falsum. Formae enim, quae sunt sicut perfectiones ultimae in natura, non intenduntur neque remittuntur et ideo etiam non commiscentur. Talem autem formam non habet elementum, secundum quod est elementum, cum elementurm diffiniatur ad compositionem, sicut patet ex praedictis, sed potius nominat formam materialem et impefectam, et ideo est remissibilis et commiscibilis forma sua. Et haec est etiam causa, quare ea retenta secundum aliquem modum susceptibile est elementum adhuc alterius formae, quia non retinet eam, nisi prout efficitur habitus confusus cum allis formis elementorum." De caelo 3.2.8 (Cologne 5,1; 241.59-80).

27. "Quia si essent formae elementorum perfecti er completi fines materiae, tunc verum esset, quod materia non esset susciptibilis aliarum formarum cum ipsis. Sed hoc non est verum, quia elementum nominat viam ad aliud, et ideo forma elementi cum allis formis salvatur in materia, sicut salvatur forma carnis in vivo, quia vivi sentientis materia propria est caro." De caelo 3.2.1 (Cologne 5,1; 221.6-13)

28. There are other indications that elements are incomplete substances. For example, the form of any element does not specify any natural shape, but any thing that is complete in species does have its own natural shape specified by its substantial form. "Quod autem dicitur, quod hoc modo [elementa] deberent etiam retinere figuras, non sequitur, quia, sicut diximus, elementa propter hoc quod sunt elementa, non habent figuras determinatas, quia figura est concomitans formam substantialem perfectam, et ideo non est vere figura nisi in corporibus animatis. In lapidibus autem est secundum minus, et ideo salvatur esse lapidum etiam fracta figura generationis eorum, quod non contingit in animatis. In elementis autem nulla est, quia elementum est ordinatum ad susceptionem omnis figurae, et ideo si haberet et retineret figuram, haberet elementum formam substantialem manentem et nullo modo commiscibilem, et corrupta figura elementi non maneret elementum, " De caelo et mundo, lib 3, tract. 2, cap. 8 (241:80-93). Elements do, however, have a sort of shape that is consequent upon the natural motions of the elements. " numquam probavimus, quod elementum haberet figuram naturalem, sicut figura est consquens formam perfectionis ultimae, sed talem habet figuram, quae est naturalis ex motu suo et loco suo. Et haec figura est, quae non accidit ei, inquantum est elementum, sed potius secundum quod est mobile ad locum ex gravitate vel levitate, " De caelo et mundo, lib. 3, tract. 2, cap. 8 (242:2-8).

29. "Et hoc esse possibile patet, si sustinere volumus opinionem Avicennae, qui, Metaph. suae tract. II, c. xi, ponit elementa in mixto remanere secundum formas substantiales quantum ad primum esse, transmutari autem quantum ad secundum, scilicet quantum ad qualitates activas et passivas: est enim mixtio miscibilium alteratorum unio. Unde possibile est materiam esse sub forma substantiali sine hoc quod habeat qualitates activas et passivas in sui complemento: et sic cum esse primum naturaliter praecedat esse secundum, expressus est ordo naturae in successione temporis, dum res prius fiunt in esse primo quam perficiantur in esse secundo." Scriptum super librum 2 Sententiarum, d. 12, q. 1 a. 4, sol. (Mandonnet-Moos, 315).


"Impossibile est enim materiam secundum idem diuersas formas elementorum suscipere; si igitur in corpore mixto forme substantiales elementorum saluentur, oportebit diuersis partibus materie eas inesse. Materie autem diversas partes accipere est impossibile nisi preintellecta quantitate in materia, sublata enim quantitate substantia indiuisibilis permanet, ut patet in I Phisicorum; ex materia autem sub quantitate existente et forma substantiali adueniente corpus phisicum constituitur: diuerse igitur partes materie formis elementorum subsistentes plurium corporum rationem suscipiunt. Multa autem corpora impossibile est esse simul; non igitur in qualibet parte corporis mixti erunt quatuor elementa: et sic non erit uera mixtio sed secundum sensum, sicut accidit in aggregatione corporum insensibilium propter paruitatem." De mixtione elementorum (155.18-35).

31. "Quidam autem utrasque rationes vitare uolentes, in maius inconueniens inciderunt: ut enim mixtionem ab elementorum corruptione distinguerent, dixerunt formas substantiales elementorum aliqualiter remanere in mixto. Sed rursus, ne cogerentur dicere esse mixtionem ad sensum et non secundum ueritatem, posuerunt quod forme elementorum non manent in mixto secundum suum complementum sed in quoddam medium reducuntur; dicunt enim quod forme elementorum suscipiunt magis et minus et habent contrarietatem ad invicem. Sed quia hoc manifeste repugnat communi opinioni, et dictis Aristotilis dicentis in Predicamentis, quod substantie nichil est contrarium et quod non recipit mgis et minus, ulterius procedunt, dicentes quod forme elementorum sunt imperfectissime, utpote materie prime propinquiores, unde sunt medie inter formas substantiales et accidentales, et sic, in quantum accedunt ad naturam formarum accidentalium, magis et minus suscipere possunt." De mixtione elementorum (156.53-73).

32. "Hec autem positio multiplicitur improbabilis est. Primo quidem quia esse aliquid medium inter substantiam et accidens est omnino impossibile: esset enim aliquid medium inter affirmationem et negationem. Proprium enim accidentis est in subiecto esse, substantie uero in subiecto non esse; forme autem substantiales sunt quidem in materia, non autem in subiecto: nam subiectum est hoc aliquid, forma autem substantialis est que facit hoc aliquid, non autem presupponit ipsum." De mixtione elementorum (156.74-84).

33. "Oportet igitur alium modum inuenire, quo et ueritas mixtionis saluetur, et tamen elementa non totaliter corrumpantur, sed aliqualiter in mixto remaneant.

Considerandum est igitur quod qualitates actiue et passiue elementorum contrarie sunt ad inuicem, et magis et minus recipiunt. Ex contrariis autem qualitatibus que recipiunt magis et minus, constitui potest media qualitas que sapiat utriusque extremi naturam, sicut pallidum inter album et nigrum, et tepidum inter calidum et frigidum. Sic igitur remissis excellentiis qualitatum elementarium, constituitur ex hiis quedam qualitas media que est propria qualitas corporis mixti, differens tamen in diuersis secundum diuersam mixtionis proportionem; et hec quidem qualitas est propria dispositio ad formam corporis mixti, sicut qualitas simplex ad formam corporis simplicis. Sicut igitur exrema inueniuntur in medio quod participat naturam utriusque, sic qualitates simplicium corporum inueniuntur in propria qualitate corporis mixti. Qualitas autem simplicis corporis est quidem aliud a forma substantiali ipsius, agit tamen in uirtute forme substantialis; alioquin calor calefaceret tantum, non autem per eius actionem forma substantialis educeretur in actu, cum nichil agat ultra suam speciem. Sic igitur uirtutes formarum substantialium simplicium corporum in corporibus mixtis salvantur.

Sunt igitur forme elementorum in corporibus mixtis, non quidem actu sed uirtute. Et hoc est quod Aristotiles dicit in I De generatione: Non manent igitur - elementa scilicet in mixto - actu ut corpus et album, nec corrumpuntur nec alterum nec ambo: saluatur enim uirtus eorum." De mixtione elementorum (156-157.119-153).