Disputationes metaphysicae

1. Reasons for doubting.—The reason for doubting is, first, because substantial forms cannot be known by any experience, nor are they necessary for all the actions and differences of things which we experience; therefore they are not to be introduced without cause. The antecedent is evident, because fire, for example, is sufficiently understood to be constituted in its being if we conceive a certain substance having perfect and supreme heat conjoined with dryness, even if the substance subject to these accidents is simple; and this is also enough for every action of fire which we experience, and for the distinction between fire and water, and for the transmutation of one into the other, which seems to consist in this, that that substance passes from supreme cold into supreme heat, and conversely. This, therefore, is enough for the constitution, distinction and action of the elements; therefore the same will proportionally suffice for the composition of mixed bodies, for these are procreated from the mixture of the elements.

2. Secondly, a repugnance seems to be involved when a form is called informing and substantial; for either it is a subsisting thing needing no sustaining subject, or it needs it; if the first, it cannot be an informing form, because it is repugnant that what is subsisting be received in another. If the second, it is an inhering form; therefore accidental; there is not, therefore, a substantial form.

3. Thirdly, because, substantial forms being posited, it cannot be understood in what way the transmutations and generations of things come about unless something comes about from nothing, which cannot be according to natural principles. The sequel is evident, because either the substantial form pre-exists generation, or something of it, or nothing. The first cannot be said, otherwise infinite forms would pre-exist in matter, and in the thing nothing would come about anew, but would appear. Nor yet can the second be said, both because in the same part of matter there cannot be something of the form without the whole form being there, since it is indivisible; and also because, even if part of the form pre-exists and part is to be induced, this part will come about from nothing; for it cannot come about from the worse part; it remains, therefore, that the third be said, which nevertheless is repugnant and exceeds the power of natural agents.

4. The ancient philosophers did not know substantial forms.—In this question almost all the ancient philosophers were ignorant of substantial forms, as is evident from what we reported above of their opinions about prime matter or the first subject of natural transmutations; for, since they thought that that subject is a complete being in act, they could not recognize substantial form; for substantial form and prime matter which is pure potency are as it were correlatives. Some also of the later philosophers, at least in the elements, denied substantial forms. So Alexander of Aphrodisias indicates, Metaphysics XII, comm. 12, although there he seems to speak only by way of example and according to proportion; and Philoponus, De generatione II, comm. 7; and earlier Galen held the same opinion, De elementis I; and before that Empedocles thought the same, who did not deny the forms of mixed bodies but of the elements, as Aristotle indicates, Physics I, text 51, and Physics II, text 22.

Resolution of the question

5. It must be said, however, that all natural or corporeal things consist of substantial form (besides matter) as an intrinsic principle and formal cause. This is the opinion of Aristotle in innumerable places, who often reproves the ancient philosophers because, substantial form being almost passed over, they applied their whole inquiry to matter, as is evident from the whole of Physics I, and Book II, c. 1, where he says that form is a more perfect nature than matter. He has the same in De partibus animalium I, c. 1, and Metaphysics VII, c. 4, and Book XII, c. 2, where he calls form a this something, because it completes substance, which is a this something; and in the same places, especially Metaphysics VII, he calls form the what it is; and gives the reason, because it is that which constitutes and distinguishes the essences of things. Moreover, De Anima II, c. 1, he distinguishes substance into matter, form and composite, and calls form ἐντελέχεια, of which name Fonseca writes many things learnedly, Metaphysics I, at the end; commonly, however, writers teach that the word entelechy is more general and comprehends more than substantial form; for it properly signifies perfection, or act perfecting a thing. But by antonomasia it is wont to be attributed to substantial form, because it is the chief act and the greatest perfection of the substantial thing. By other names too substantial form is wont to be named by Aristotle, which we shall note below in explaining its causality. Yet Aristotle was not the discoverer of this truth, for before him Plato recognized substantial form, as is evident from the Timaeus, where he calls forms images of the truly existing, that is, participations of the ideas, while he himself posits ideas only of substances. And before Plato some of the philosophers are believed to have touched upon substantial forms, as is evident from Aristotle, De partibus animalium I, c. 1, and other places cited above. And now this dogma is so received in philosophy that it cannot be denied without great ignorance; and it is so consonant with the truth of the Christian faith that its certitude is not a little increased thence; wherefore it pleases me to begin the proof of this truth from a certain principle certain by faith and evident by natural light.

From the rational form the other substantial forms are gathered

6. Let the first reason, then, be: man consists of substantial form as an intrinsic cause; therefore also all natural things. The antecedent is proved, for the rational soul is a substance and not an accident, as is evident, because it remains per se separated from the body, since it is immortal; it is therefore per se subsisting and independent of a subject; it is not, therefore, an accident, but a substance. Again, that soul is the true form of the body, as faith teaches and is also evident by natural light; for it cannot be a substance assisting or extrinsically moving the body, otherwise it would not vivify it, nor would the works of life depend essentially on its presence and conjunction; nor finally would it be the man himself who understands, but some other assisting substance. Man, therefore, consists of body as matter and rational soul as form; this soul, therefore, is a substantial form; for, as we shall declare below, by the name of substantial form nothing else is signified than a certain partial substance which can be so united to matter that with it it composes a substance integral and per se one, such as is man.

7. But the first consequence is proved, supposing that the discussion is of natural generable and corruptible things, for these as regards this part are of the same order with man, and among them there can be transmutation and vicissitude; but thence it will easily be concluded a fortiori that the same is to be said of incorruptible bodies, supposing the opinion which we treated above about their matter. The composition of man, then, from matter and substantial form shows that there is in natural things a certain substantial subject by its nature apt to be informed by some substantial act; therefore such a subject is imperfect and incomplete in the genus of substance; it seeks, therefore, always to be under some substantial act. But this subject is not proper to man, but is found also in other natural things, as is self-evident; whence it is supposed both for the generation of man and for nutrition, and remains after his corruption; therefore all natural things which consist of that subject or matter consist also of substantial form actuating and perfecting that subject. Moreover, from the same composition of man it is gathered that an aggregation of several faculties or accidental forms in a simple substantial subject is not enough for the constitution of a natural thing; for in man there are those faculties and accidental forms, perhaps more and more perfect than in other natural things, and yet they do not suffice for the constitution of some complete natural being, but there is required besides a form which as it were presides over all those faculties and accidents and is the fountain of all the actions and natural motions of such a being, and in which that whole variety of accidents and powers has its root and a certain unity; therefore by the same reason in the other natural beings there is necessary some substantial form distinct from accidents and more intimate and perfect than they. Thirdly, by the same example it is evident that the substantial generation and corruption of man does not consist in the acquisition or loss of some accidents, but in the union or disjunction of the rational soul substantially informing the human body, to which certain accidents prepare, which being taken away, the soul recedes and the man is corrupted; therefore in the same way the corruption and generation of other natural beings is to be understood to come about. For, as far as can be gathered from experience, the same mode of generation and corruption is in other things as is in man, except the difference in the perfection and subsistence of the human form, which we would not gather from the mode of generation and corruption unless it were known to us from elsewhere. And on that account it is said in Ecclesiastes 3: The death of man and of beasts is one, and the condition of both is equal; as man dies, so they also die, etc. Finally all the indications and signs of substantial composition which can be thought out in man are in the other natural beings, and especially in animals, as will be evident from the following reason.

Various indications of substantial form

8. The return of an altered patient to its pristine state.—The second principal reason, then, is taken from various indications arising from the accidents and operations of natural beings, which indicate that substantial form lies hidden beneath them. The first is seen even in the elements; for if water, for example, is heated, and afterwards the agent is removed, it is brought back from within to its pristine coldness, as is evident by experience; therefore it is a sign that there is in the water some more intimate principle from which again the intension of cold emanates, extrinsic impediments being taken away; but that principle can only be the substantial form; therefore. The first consequence is proved, because there can be no extrinsic principle of that reduction, both because, if that reduction were from without, it would not be per se and necessary, but by accident, as an extrinsic agent happened by chance to occur; and also because, running through all the extrinsic principles which commonly occur, there is none from which that action could come; for proximately only the surrounding air is wont to occur, which either naturally is not as cold as water, or by accident is wont to be left as hot as the water itself; whence it too brings itself back to its pristine state as far as it can; but remotely only heavenly and universal causes intervene, which of themselves are not determined to an action of this kind, as is known.

9. Various causes of such reduction are refuted.—But the second antecedent, namely that no other intrinsic cause of that action can be thought out besides the very form of the water, is proved, for what will that be? Some say that in some parts of the water intense cold always remains, and that from those parts the others which were heated are cooled, which Cajetan thinks probable, I, q. 54, a. 3; and it is attributed to Averroes, De Anima II, comm. 1. But this is frivolous and against experience; for we perceive by sense that the whole water poured into some vessel is very hot, from whatever part it is touched; but if there were some parts so cold, either they would be perceived by sense, or at least they would temper in some part of the water the sense of heat; but neither happens. It is also against physical reason, for the whole water according to all its parts is uniformly-difformly applied to the fire acting naturally; therefore according to all its parts it undergoes uniformly in the same way; for what is there which could either impede that action or so interrupt it that it would come about in some parts and not in others? Likewise, either those parts which are said to retain cold can be heated, or not; if not, then neither could they be corrupted; but if they can be heated, then, if the whole water is sufficiently applied to the fire, those too will be heated, or certainly a state can be given in which that potency is reduced to act, and, that being posited, the water will still be brought back to its pristine coldness, the contrary agent being removed, provided it has not come to the corruption of the water.

10. Others answer that that action does not come from any principle distinct from coldness; for coldness always remains in some degree, and itself, as soon as it is not impeded, recalls itself to its pristine state. For in coldness itself two things can be distinguished, namely the essence and the mode of intension; and the essence always remains integral, even if the intension is diminished, and therefore from the same essence the mode of intension can emanate. But this answer too is false. First, because from a remiss quality a more intense degree cannot proceed; otherwise air too would make itself supremely hot, and so of all other things. Secondly, because it often happens that there are more degrees of heat in the water than of cold; therefore, even the extrinsic agent being removed, the coldness could not overcome the intense heat, because it would in no way be helped by the subject, since matter alone of itself is indifferent to each accident. Thirdly, because otherwise cold and heat in remiss degrees could never remain quiet in the same subject, but always one quality would expel the other, perfecting itself up to the ultimate intension, because on the side of the subject (if it were matter alone) there would be no impediment, and we suppose that all other extrinsic things are taken away.

11. In the elements no qualities virtually contain the first qualities.—Others finally answer that there is indeed necessary another internal principle prior to coldness, which remains integral even if the coldness is remitted, from which that reduction is derived; but they deny that that principle is the substantial form, for from it alteration could not immediately come, but they say it is a certain quality of a superior notion, virtually containing the first sensible qualities. But this opinion can be understood in two ways: first, not denying the substantial form, but positing that virtual quality intermediate between the substantial form and the first sensible qualities, and in this sense it is not repugnant to the truth which we intend to prove; yet it weakens the reason which we are pursuing, and moreover is to be rejected as superfluous and gratuitously feigned, for it multiplies qualities without foundation or any experience, for the emanation of an accident from the intrinsic form does not need another intermediate accident; otherwise one would proceed to infinity. Likewise, because it is repugnant that there be given in the elements any qualities prior to the first; but the first qualities of the elements, on the testimony of Aristotle, are formal heat, coldness, etc. Whence, although perhaps in mixed bodies there is sometimes given a quality virtually containing heat or cold, nevertheless that is both posterior to the temperament of the first qualities connatural to the mixed body and is not for the intrinsic emanation of the first qualities in the same subject, but for effecting by proper action in extrinsic subjects. That answer can be understood otherwise, so that it intends to take substantial form out of the way and in its place posit a quality. But understood in this sense it is easily refuted, because that quality is not immediately and per se sensed, but is discerned from this effect of natural emanation; on what foundation, then, is that internal principle said to be an accidental quality and not a substantial form? Likewise, that principle is the first act of matter, completing with it this natural being which we call water; therefore it is substantial act and not accidental. Likewise, that form is not only the root of cold but also of humidity, density and the other properties which the element of water requires; for of them the same argument can be made, that if through contrary action they are changed from that natural state which water postulates, as soon as the contrary recedes they return to the natural state; therefore they have another prior form from which they are derived, which remains unchanged; therefore either to each correspond individual radical (so to speak) or virtual forms, which nature abhors and is altogether superfluous, or there is one form in which all those properties are rooted and as it were bound together, which is most true; therefore that form is not accidental but of a superior order. It is, therefore, the substantial form from which such a reduction comes, as the common opinion holds, of Avicenna, Sufficientia I, c. 5; Soncinas, Metaphysics IX, q. 8; Soto, Physics II, q. 1, and others.

12. And hence can be taken another indication, which is a confirmation of the preceding; for by almost evident experience it is established that even in these inanimate things or elements substantial corruption is distinct from alteration; I speak specifically of inanimate things, in order that the induction may be universal a fortiori; since in animate things the matter is more evident, as will be evident. We experience, then, that alteration, for example the heating of water or iron, is sometimes so vehement that most intense heat is sensed in them, and nevertheless, if the action of the contrary agent ceases, those things remain either integral or almost integral in their substance, and easily also return to their accidental state; but sometimes the alteration proceeds so far that a complete transmutation of the thing comes about, so that, although the agent is removed, that patient can never return to its pristine state nor recover its prior actions or similar accidents; sometimes too it is changed into a viler sensible substance, as ashes, slag, etc.; but sometimes it is altogether consumed insensibly, because it is transformed into another subtler and insensible body; therefore it is an evident sign that alteration is sometimes pure and remains within the breadth of accidental change, but sometimes has conjoined a greater change of the thing. But this can be nothing else but because the substantial composite itself is dissolved, the substantial form receding; there are, therefore, substantial forms. The last subsumption is proved, because, if the whole substance of the thing always remained equally integral, however far the alteration proceeded, it of itself would always have the same relationship to the accidents; therefore either it would always remain quiet after any alteration whatever under any accidents whatever, as far as depended on itself and the contrary agent being removed, or certainly, the same agents being removed, it would always return to the same accidents.

13. And this reason is confirmed, for we see that some accidents are so inseparable from some subjects that, if they are taken away or too much diminished, a complete transmutation comes about in the subjects, so that they cannot by intrinsic power return to their pristine state; therefore that inseparability comes from the connection of such accidents with some internal principle of such things. Which cannot be prime matter or that first subject which remains under every transmutation, because with respect to it no accident is inseparable of those which can be acquired or lost through alteration. Nor yet can that principle be some accident, if the discussion is of the first and radical principle; for, although one accident is inseparable with respect to another, as rarity with respect to heat, or whiteness with respect to such a temperament of the first qualities, nevertheless that temperament is inseparable from another prior form left to its nature; one must necessarily stop, therefore, at some form which is first with respect to the inseparable accidents; that, therefore, is the substantial form and not an accidental, since it constitutes the proper essence in which such accidental properties are connaturally and inseparably.

14. The subordination of properties among themselves an indication of substantial form.—Finally another reason can be formed from this indication, because in one natural being many properties are conjoined, which sometimes are so subordinated among themselves that one arises from another, as the will from the intellect; but sometimes they do not have subordination among themselves, as heat and humidity in air, whiteness and sweetness in milk, or several senses in an animal; therefore this multitude and variety of properties, especially when they are related in the latter way, requires one form in which all are united; otherwise they would be merely accidentally gathered in the same subject, and, one being altogether taken away, another would not on that account recede; but the opposite is evident by experience; therefore it is a sign that such accidents, in such number, weight and measure required in such a subject and being, do not have that connection with respect to the first subject alone or prime matter, but with respect to some composite which by reason of the form requires that order of accidents among themselves. And this reason is wont to be specially confirmed in mixed bodies, in which we see contrary accidents reduced to certain degrees preserved in the same mixed body; but this cannot come from the qualities themselves, as is sufficiently self-evident, since by their nature they rather fight. Nor yet does it come from an extrinsic cause nor from matter, as is easily evident; therefore it must come from the form. But this confirmation either has no force at all, or is not a reason distinct from the preceding, for the four first qualities, reduced to that temperament in which they can be at the same time in the same subject so as to be perpetually preserved in it in the same state, do not need another internal cause or principle, but only the removal of the extrinsic corrupting agent, because those qualities constituted in that degree are neither properly contrary nor can have action among themselves; indeed, if they could have it, the substantial form could not impede or reconcile it. Whence it comes about that in living things, even in man, where the form is supremely one, it cannot impede action between heterogeneous parts, because, although in the individual parts the qualities are so tempered that they agree among themselves with respect to their proper subject, they are not so tempered with respect to the qualities of another dissimilar part. From this preservation of a temperament consisting of contrary qualities, then, precisely taken, substantial form is not inferred. Yet it is excellently inferred from this, that in such a temperament the qualities are not only permitted (so to speak) to remain in that degree, but also are so connected in it and so require it that, if one of them is extrinsically either increased or diminished, the extrinsic agent being removed, the temperament at once returns to the prior proportion, which is seen most of all in animals; this, therefore, is an evident sign that such a temperament belongs to some form in which those qualities are connected. But this sign coincides with that of the reduction of the thing to its natural state.

15. That a thing acting intensely by one faculty is remitted in the action of others is a sign of substantial form.—Lastly this reason is confirmed by another indication taken from the action of certain natural things; for we experience that a thing having several faculties of operating, while it operates intensely through one, is impeded from being able to operate through another, or not with so great effort; therefore it is a sign that those faculties are subordinated to the same form, which principally operates through them; for, if they had no subordination among themselves nor with some common principle, each of them would have its operation independently of the other, nor would there be any reason why the effort of one should impede the effort of the other more than if they were in diverse subjects; but from subordination to the same form an excellent reason is given, because, since that is of finite power, while it is intensely applied to one operation it is distracted from another, and can incline to one with so great effort that its power is exhausted there. The antecedent is declared by some in natural things or agents, which, while they act intensely to overcome a contrary, cannot altogether protect themselves from being in some part overcome or suffering from the contrary. But this experience of the reaction of natural agents does not come from the subordination of several faculties to one form, but from this, that a thing is not always as powerful to resist as it is to act. Whence even the hottest iron, while it heats water, suffers from it in return, although the form of the iron contributes nothing at all to that action; indeed there the operations of diverse faculties do not intervene, but the action of one quality, namely heat, and a passion in some part contrary to it, which comes from this, that heat is not so powerful to resist as to act. Wherefore in inanimate things I scarcely believe that any experiment can be found by which that antecedent may be proved, because in accidental actions which do not proceed from life there does not seem proximately to intervene any concurrence of the substantial form by reason of which the action of one faculty is remitted from the effort of another. But in living things, and especially in ourselves, we manifestly experience an effect of this kind; for sometimes attentive interior thought impedes our seeing even present things; indeed even prolonged meditation is wont to impede the action of the nutritive part. Nor does it matter if someone says that this comes from the concurrence of the vital spirits, which are necessary for the operations of these faculties, and, while they flow together to one, they abandon another; both because that very concurrence of the vital spirits to one faculty rather than another is a sign of one form using those spirits and faculties for two actions, otherwise there would be no reason why the spirits should flow together to one faculty more than to another; and also because intellectual operation does not come about by means of spirits, and yet effort and attention to it impedes the inferior actions. Nor can this be attributed to the cooperation of the phantasy, which requires the concurrence of spirits; for intellectual attention, especially if it is vehement and about things of a superior order, also greatly diminishes the action of the phantasy itself; therefore it does not come from the spirits, but from the occupation of the same soul about some operation.

The causes of substantial form clearly show it

16. It is not repugnant that there be substantial form.—A third principal reason can be given a priori from the proper causes of substantial form, which are the final, efficient and material; for it does not have a formal cause, since it is itself the form, whence from it no positive reason can be taken. We can, however, suppose that on its side there is no repugnance that such a genus of being or incomplete substance be given in the nature of things; for what repugnance can be feigned or thought out in this? Likewise, because it is not repugnant that there be given in the nature of things substantial acts of the supreme order which are subsisting and not informing, as angels, and a substantial act of the middle order which is at the same time subsisting and actuating or informing, as has been said of the rational soul; therefore it will not be repugnant that there be given substantial acts of the lowest order, that is, which are actuating acts and not integrally subsisting, and these we have called substantial forms. Likewise, either such an act would be repugnant because it is act, or because it is substantial, or because it is repugnant that these two be conjoined in the same thing; none of these can be said with probability; therefore neither is it repugnant that there be given a substantial form, as far as depends on its side. But if on its side it is not repugnant, it will at once easily be proved from the other causes either that it is not repugnant or even that it is necessary. The first two parts of the first antecedent seem self-evident. The first indeed, because it is self-evident that there are given in things entities which are acts and perfections of others; for so whiteness is the act of the white and intellection of the understanding. But the second, because it is also self-evident that there are given in things substantial entities, since these are the foundation of all others. The third part, then, remains to be proved, namely that it is not repugnant that these two properties or notions be conjoined in the same entity; but this is evident, both because nothing can be assigned in one of those notions which is intrinsically repugnant with the other, and also because the notion of act of itself expresses perfection; therefore, if it is not repugnant that it be conjoined with accidental being, why is it repugnant that it be coupled with substantial? And finally because, since the notion of substantial entity looks to perfection simply, it seems more repugnant to the notion of potentiality than to the notion of actuality; but the first is not repugnant, as is evident in prime matter; therefore neither will the second be repugnant. And hence a new reason arises; for potency and act correspond to each other with proportion in every genus; but it is not repugnant that there be given in natural things a substantial potency which in the genus of substance is an incomplete and imperfect being, as was shown above and is manifest from the composition of man; therefore it will not be repugnant that there be given an act proportioned to this potency, by which it can be actuated in any natural thing whatever and exist and be preserved in a way connatural to itself.

17. It is demonstrated from the material and efficient cause.—And hence the reason taken from the material cause is easily concluded; for, since matter is substantial potency, it contains in its genus and in receptive potency every act proportioned to itself; therefore it is able to cause it in its genus, if from elsewhere it is not repugnant; therefore on this side the material substantial form has a sufficient cause in order that it can be. Again the reason is concluded from the efficient cause; for, if the discussion is of the first cause, there cannot be lacking the power by which it could effect in the universe substantial forms actuating matter, either dependently or independently of it, according to the various grades and perfections of such forms, their non-repugnance being supposed; therefore, since such forms are necessary in the nature of things, they have been effected by such a cause. But if the discussion is of the proximate cause, it is to be seen afterwards which can intervene with respect to each form. Now let it suffice to say that such a cause cannot be lacking if such an effect is necessary for the constitution of natural things; whence, if sometimes this power is lacking to created causes, it pertains to the causality of the first cause to supply also the function of the proximate cause, which, speaking per se, it only does in the rational soul as regards its effecting; for to other forms, from the mode in which they come about, it is not repugnant that they come about from created agents, since they come about with the concurrence of matter, as we shall immediately explain. But whether in such agents there is sufficient power we shall say in treating of the efficient cause.

18. The chief indication of form is its end.—The chief reason, then, is to be taken from the end of the substantial form, which is to constitute and complete the essence of the natural being, which end or effect is absolutely necessary in the nature of things; otherwise there would be nothing in corporeal things complete and perfect in its substantial nature; nor would there be the multitude and variety of substantial species in which most of all consists the wonderful disposition and beauty of this corporeal universe. For this end, then, substantial form is altogether necessary, because, since matter is a very imperfect being, the integral essence of each thing cannot consist in it alone. Next, because matter, in so far as it is the first subject, is one and the same in all natural things; therefore their essence cannot consist in it alone; otherwise all would be of one essence and would differ only accidentally, which is repugnant to the amplitude and beauty of the whole universe, which arises most of all from the variety of species. Which seems to be signified in Genesis 1, in those words: Yielding seed according to its kind, or according to its species. And that repetition is often made, according to their species and in their kind, and finally it is concluded: God saw all things that he had made, and they were very good, because surely the complete goodness of the whole universe arises from that variety. Which also the various powers and operations of things and the mutual generations and corruptions sufficiently show, as has been declared. Something, therefore, besides matter must be added to it by which the essence of each thing is completed; but, since matter is potency, that which is added to it to complete the essence will be act, because potency expresses an essential order to act.

19. But that act which is adjoined to matter to complete the essence of the thing cannot be an accidental act. First indeed, because from act and potency of diverse orders an essence truly and per se one is not completed; but the essence of a natural and substantial thing must be truly and per se one; otherwise it would not be one substance. Secondly, because, since matter is substantial potency, it is not filled by accidental act; therefore with it it cannot complete the true essence of a natural thing. Thirdly, because, if such an act is accidental, I ask to what it happens. For either it happens to the composite of that act and potency as such, and this is repugnant, because, since that composite intrinsically consists of such form, it cannot happen to it; in which way too whiteness is not an accident of the white as white, but of the white subject. Or it happens to matter or the substantial subject, and so I ask again why it is said to happen to it. Either because matter can be with such act and also without it. And this is not enough; otherwise the rational soul too would be an accident of the body; this, therefore, can be common to substantial act as well as to accidental. Or it is because such form depends on matter in its being, and this too is not enough, because even parts of substance can depend on other parts, and matter itself depends in its way on form; there are, therefore, various modes of dependence, and it is not repugnant to some incomplete substance to depend on a subject of the same order. Or finally it is called accident because in its being it has an entity so imperfect and diminished that it is of an inferior order than the whole breadth of substance. And this first of all is said gratuitously and without foundation; for whence is it evident that that act of matter, to which it is primarily and per se ordered and which with it completes the essence of the natural thing, is so diminished and incomplete an entity? Next it is repugnant to the end of such form, because, as I said, one substantial essence cannot be composed of a substantial subject and an accidental form, especially since the form is that which gives the ultimate grade and complement of the essence. On account of which Aristotle rightly said, Physics I, c. 6, that substance is not composed of non-substances; but it is evident that natural things and their essences are substantial and per se one; the philosophical dogma of substantial forms, therefore, is most certain.

The arguments are solved

20. Of the reasons for doubting posited at the beginning, the first two remain solved from what has been said. For to the first it is denied that sufficient indications and effects are lacking in natural things, through which one can sufficiently arrive at the knowledge of substantial forms, and it is consequently denied that all actions or transmutations can be saved without substantial forms. To the second it is denied that it is repugnant that some form be subsisting and informing, either in diverse states or even in the same, as we shall declare more fully below in treating of subsistence. It is also denied that it is repugnant to be a form dependent on a subject and to be substantial, as was said a little before; but how this dependence differs from the inherence of an accident we shall say in the following disputation. But in the third argument a special difficulty is sought, which it is necessary to treat in the following section.