Disputationes metaphysicae

1. Difficult reasons for doubting.—The first.—The reason for the difficulty can be taken, first, from what was said in section 4, where it was shown that the agent sometimes acts on itself even according to the same part; but the same thing cannot be unlike itself according to the same part; therefore it is not necessary that the patient always be unlike the agent. It will perhaps be said that, when something acts on itself, it always operates through a power of another notion than the form which it makes in itself, and so at the beginning of the action it is unlike itself, inasmuch as it does not have that form formally, but only virtually.

2. The second.—But against this I argue, secondly, that something sometimes acts on itself even through the same quality formally; for the heat or cold of some body, when it is surrounded by a contrary agent, is commonly wont to intensify and as it were fortify itself in order to resist or overcome the other, as is evident in the heat of the stomach, which for this reason is stronger in winter time, as experience shows and as Hippocrates testifies, aphorism 15. The same is evident in air existing in caverns or very low places, which is warmer in winter time. Nor can this be attributed to an extrinsic agent, since that is contrary and cannot intensify a quality opposed to itself. Nor can it be attributed to natural emanation from the intrinsic form, both because this of itself is always the greatest that can be, since it is merely natural, nor is there any reason why it should be increased on account of a surrounding contrary—indeed it ought rather to be impeded by it—and also because that mode of action is found not only in a natural subject but also in a preternatural one, for water too in wells becomes warmer in winter time.

3. The third.—Thirdly, there is a similar argument: one thing sometimes acts on another like itself in quality and intensity, even though the action takes place through the same quality. The assumption is evident from the common example of iron, which, although it does not have in itself supreme heat, but as six, for example, intensifies like heat in straw or tow so that it burns it. And in the same way the heat and light of the medium are commonly intensified by reflection from the heat or light of the extremely distant body, even if that is not in itself hotter or brighter intensively; as when the sun directly heats the air and the earth, the heat of the air is intensified by the reflection of the earth, and similarly the light of the air is intensified by the reflection of a mirror, etc., although neither the heat in the earth nor the light in the mirror could be more intense than in the air from the action of the sun, since they are more distant from the sun than the air.

4. The fourth.—Fourthly, if this unlikeness were necessary for any cause, it would chiefly be in order that the agent might surpass the patient in power of acting; but it is not necessary for this cause, both because it can happen that that superior power comes from elsewhere, namely from greater density or from other conditions of the subject, and especially because that excess on the part of the agent does not always seem necessary; otherwise the patient could never react upon its agent. For either it is surpassed by it in power or not; if it is not surpassed, and nevertheless suffers from it, then excess of power is not required in the agent; but if it is surpassed, and nevertheless reacts upon it, then excess of power is not required for reacting; but reaction is true and proper action and effective causality; therefore for this excess of power is not always necessary; therefore neither is unlikeness in form or in the notion of acting. Finally, it can happen that an action is coeval with the agent, as illumination with the sun; but then there never intervenes unlikeness between agent and patient, because they were always alike.

Notes for the resolution of the question

5. Unlikeness between agent and patient is to be considered for the beginning of the action.—It must be noted that, when we ask whether the efficient requires a patient unlike itself, the discourse is not of the end of the action, but of the beginning, or of the disposition and proportion which must precede between agent and patient for the action; because here we are inquiring into the conditions required for acting, not those which follow upon action. And moreover, because at the end of the action the patient will not so much be compared to the agent as the effect to the cause. Whence it comes about that unlikeness in the terminus of the action cannot be of the notion of efficient cause, since rather the intention of the agent is to render the patient like itself. But if sometimes it does not perfectly attain this, it comes from the imperfection of the effect; and this sometimes arises from the weak power of the agent, which cannot overcome the resistance of the patient; sometimes from the incapacity of the patient and the nobler power of the agent, which is universal, or an equivocal cause acting through a form of a superior order, which the effect cannot receive according to the same notion, and therefore it becomes like according to some analogy or common notion, but not perfectly.

6. The action can be coeval with the thing which acts.—Again, it must be observed that, when we inquire into the unlikeness which must precede between patient and agent, the discourse is not of antecedence in time or duration, but in the order of nature and causality; for the former, although it often intervenes, is not per se necessary, as the last argument made at the beginning rightly convinces. For there is no doubt that an action can be coeval with the agent when it does not require succession and takes place without resistance. Hence, if it is a natural action and of its species such that it can render the patient perfectly like the agent, it will accomplish that likeness from the beginning; for a natural agent, as soon as it exists, acts as much as it can; and therefore, if it acts without resistance, it produces a perfect effect from the beginning; therefore according to real duration in that action the patient is never unlike the agent. Nevertheless in the order of nature it can be understood as unlike, because such a patient of itself, the action of the agent set aside, would not have likeness with it. And so that action does not take place about the patient as already like, but rather renders it like; and thus it takes place formally from the unlike.

Resolution of the question

7. Each thing acts on what is unlike in form and like in matter.—The sense of the question being thus explained, its resolution is easy; for it must be said that an acting cause cannot effect in a patient except inasmuch as it is unlike itself in form or in the terminus of the action. This is as it were a first principle in philosophy; Aristotle hands it down, I De Generat., c. 7, text 46, where he says that the greatest part of the ancients affirmed with the utmost agreement of mind that nothing like suffers anything from what is like, because the one is in no way more active or passible than the other. And in text 48 he confirms the same, because otherwise by the same reason the same thing would be affected by itself. Which he declares in what follows, saying that this unlikeness is necessary according to form or species, for in the matter or subject-genus likeness rather is required between agent and patient, which we shall declare a little below. Aristotle supposes the same principle in the same bk. I De Gener., c. 9, when he says that the agent acts inasmuch as it is in act, and the patient suffers as it is in potency. Which he also teaches throughout bk. I Phys., and bk. III at the beginning, and bk. VII from text 35, and bk. VIII from the beginning. And the expositors in these places generally think so, although some in certain particular actions do not declare it rightly, as we shall see in answering the difficulties.

8. The reason for the conclusion.—Absurdities from the opposite of the conclusion.—The reason, however, has been touched upon: because the agent acts inasmuch as it is in act, and for acting requires a patient which is in potency; but that which is in potency, as such, is unlike that which is in act, as such; therefore. The major as to its first part is established, because to act is to communicate or give being, and therefore it is necessary that such being be supposed actually in the cause, either formally or eminently, according to the mode and dignity of the agent; for no one can give what he does not in some way have in himself. And by almost the same reason the other part of the same proposition is proved, because, while the agent communicates its being to the patient, it brings it from potency to act; therefore the patient, as it underlies such action, is supposed in potency. And therefore in I Phys. privation is placed among the principles necessary for generation on the part of matter, which principles are proportionally necessary in every change or action which takes place from a subject. Aristotle also excellently confirmed the conclusion from the drawbacks: because otherwise there would be no reason why of two like things one should act on the other rather than conversely. Likewise, because the same thing could intensify itself. Likewise, there would be no end of actions, but after a perfect fight between contraries, victory gained and the patient assimilated, the action would then be begun anew. And finally, as Aristotle says, in this way nothing could be preserved either from perishing or from motion.

Corollaries from the preceding resolution

9. And from these reasons it follows, first, that the unlikeness per se necessary between acting and suffering cause is only that which is between habit and privation, or between a thing constituted in act and one existing in potency; for if in the patient there is supposed capacity to receive the form, and the agent has the power to produce it, it requires no other unlikeness on the part of the patient except that it lack such a form; because neither from the notion of motion or action nor from any other general principle can another be universally required. Hence, that in generable and corruptible things there is found not only this unlikeness but also positive opposition and contrariety is not from the notion of efficient cause as such, but from the fact that such things have been so instituted that they can have mutual fight and action among themselves, and be generated and corrupted from one another according to species. It must be noted, however, that among efficient causes some are univocal, others equivocal, which words we have already explained above; we are treating, however, of principal causes, for from them it is easy to accommodate the doctrine to instrumental ones. In univocal causes, then, the said condition intervenes most properly and formally; for since the agent introduces into the patient a form of the same notion as that through which it acts, it supposes in the patient the lack of it, and consequently supposes formal unlikeness with it.

10. But the equivocal cause does not introduce into the patient a form of the same notion, and hence formally like its form through which it acts; and therefore it does not properly suppose in the patient formal unlikeness, that is, lack of that form according to the species which it has in itself; but it supposes unlikeness between the patient as it underlies the action and as it is perfected by the action, and consequently it also supposes in the patient the lack of that likeness which can intervene between some form formally taken and another which eminently contains it. And the reason is clear. First, the equivocal cause does not make formal likeness, but only eminential (so to speak); therefore it prerequires only proportional unlikeness; for only the privation of the form which terminates the action of the agent is necessarily supposed for the action. For it is not required for action that the patient lack the form which is formally in the agent, if it is not going to receive it formally or of the same notion; but it is only necessary that it lack that form which is to be introduced into it and is going to be the terminus of the action, even if in the agent it is only virtually or eminently; because the privation required for action is not formally opposed to the form which is the principle of the action, but to that which is going to be the terminus ad quem of the action, since such privation has the notion of terminus a quo. Thus, then, the unlikeness necessary between an agent of this kind and the patient need not be formal, but eminential suffices, as has been declared. And for this reason one heavy thing can move another downward, even if they are alike in gravity, or even if they are moved downward together and in this too are alike, because the formal terminus of that motion is not gravity but a lower Ubi, which is in a certain manner contained virtually in gravity; and therefore the privation of that, not the privation of gravity, is necessary for that motion. And the same holds of all similar cases, especially in immanent acts, in which the action of the power is always equivocal, of which it is commonly said that it does not so much tend to producing what is like as to producing what is proportional, that is, a second act consonant with the first and which is its perfection, in which it is contained not formally but virtually and eminently. And therefore in that action too, between the active and the passive principle, as such, only the said eminential unlikeness is supposed, namely, that in the one is eminently contained the act which the other does not have formally until it receives it from the active principle; which unlikeness is always found, whether those principles are distinguished in reality or only in reason, as will be more evident in the solution to the first.

11. From what heads there is no action between two things.—The first.—The second.—It follows, secondly, from what has been said, that for efficiency per se it is required that the acting cause have power over the patient and about its capacity, because otherwise it would be impossible for action to follow. This follows from what has been said; for on this account the aforesaid unlikeness between agent and patient is necessary, in order that in the agent, inasmuch as it is in act, there may be power to subject to itself the patient, which is only in potency. And it is confirmed, for just as it is impossible for a form to inform matter unless it has an informative power proportioned to the matter, so neither can an agent in its genus actuate a subject unless it has power over it, because universally second act requires proportioned first act. In order, however, that this may be declared more fully, it must be noted that it can arise from four heads that action does not follow between some two things—I speak of natural agents. First, if there is no active power in them. Secondly, if in the one there is power, but in the other there is not capacity for that form which the other can make; for which cause fire cannot heat the heaven; and therefore Aristotle did not posit negation as a principle of generation or change, but privation, because it must be in a capable subject. Therefore too he said, in I De Gener., that between agent and patient there is required unlikeness in form and likeness in matter, by reason of which the patient is capable of the form of the agent. Which, however, is not true in the same way in all agents; for the heaven acts on these lower things although it does not agree with them in matter, and an intelligence moves a body with which it does not agree in matter. In agents, then, which act by univocal and corruptive action that proposition is simply true, and of them Aristotle properly spoke; for in the same place he said that the agent which agrees with the patient in matter also suffers from it, but that it is otherwise of a superior agent, which does not communicate in matter. In agents, then, acting by equivocal action, only that agreement according to some common notion is required; for we are speaking of created agents, among which none can alter or generate another unless they agree in some way in matter, at least in general, because both must be material. In local motion too this is found, that mover and moved always agree in some way in the capacity of receiving motion proportioned to them; for nothing created can move locally unless it is itself also mobile, as is established of bodies, and of the intelligences too we shall say below. But this is in a certain manner extrinsic to the notion of agent; what is intrinsic, however, is that there be in the patient capacity for that form of which the active power is in the agent.

12. The third.—Thirdly, action will be impeded if that capacity has already been reduced to act, because then too the power of the agent over the patient ceases, since whatever could be done by it has already been done; which coincides with what we have said so far, namely, that nothing can act on what is like itself inasmuch as it is such; which is as true in univocal agents as in equivocal ones, speaking of the proportioned likeness which can be between them and their effects, as is established from the foregoing. For the proportional reason arises from this same root, namely, because the whole power of such a cause has already been fulfilled in such a patient, and therefore nothing remains for it to do. You will say: even if the patient is in act through one form or quality, there can still remain in the agent power to introduce another like it; otherwise this whole question will be reduced to that one, namely, whether two accidents differing in number alone can be in the same subject. I answer that it cannot, because after the capacity of the subject has been completed by one act, it no longer remains in potency to another like act; and as to this it is true that this question is very closely conjoined with that about several accidents differing in number alone in the same subject. For if in the same matter there could be several substantial forms, differing either in species or in number, a natural agent could introduce another form into matter which had only one; therefore similarly, if a subject could have two wholly like accidents, although it had one, it could receive another from a like agent, or even from itself; and therefore we said above, disp. V, sect. 9, that accidents diverse in number alone and wholly alike cannot be received together in the same subject.

13. The fourth.—Fourthly and finally, power on the part of the agent and capacity in the patient being supposed, with unlikeness and privation, action can still be impeded on account of the resistance of the patient. In which it must be observed that for action as such resistance in the patient is not per se required, just as we also said that contrariety or positive opposition is not necessary; for privation as such does not resist, but rather prepares the way for action; whatever, therefore, resists is reduced to positive contrariety or repugnance, and therefore it is not per se required for action, but rather of itself impedes or retards action. Hence, that an action is successive and not instantaneous comes from the resistance of the patient, unless local motion intervenes, to which such succession is intrinsic, as is established from philosophy and as we shall touch upon below in the treatise on action and passion. Hence, then, it comes about that, when beyond the unlikeness of the patient resistance also intervenes, if it is so great that it either surpasses or equals the power of the agent, the action is impeded; and therefore it is a common axiom of philosophers, and as it were a first principle, that for effecting a proportion of greater inequality is necessary, that is, one in which the power in the agent is greater than the resistance in the patient. Which is taken from Aristotle in the places cited, and is easily evident, because the agent as agent overcomes the patient, at least as to that which it does; therefore it is necessary that according to that notion it surpass it in strength; otherwise how could it overcome? And this will be declared more fully in the solution of the fourth argument.

Solutions of the arguments

14. It remains, then, that we satisfy the arguments; and to the first it was rightly answered there, and from all that we have said the answer has been declared, and can be declared further. For the same thing can at once and according to the same part be in first act and in potency to second act, which others call being in virtual act and formal potency; and so according to those two notions, whether they are distinguished in reality or only in reason and relation, it has to itself a certain unlikeness, not proper and formal, but eminential and virtual, which is enough for action, as we have said.

On antiperistasis

15. The opinion of some.—In the second argument the common difficulty about antiperistasis is raised, which is purely physical and is commonly treated ex professo in I De Generat., c. 7; and therefore I shall touch on few things necessary in this place. Some, then, say to that reason that, although the same quality cannot intensify itself by direct action, it can by reflected action, which they say intervenes in that case in this way: that the hot thing, for example, besieged by its contrary, sends certain species into it, which are as it were instruments for acting on it; but since the contrary itself resists those species, they are reflected onto their agent, and so intensify it. So teach Marsilius, I De Gener., qq. 17 and 18; Albert of Saxony, q. 15; Paul of Venice, in the Summa on Generation, c. 23, and in the Summa of the Meteorology, c. 3; and others. But this opinion says incredible things and does not solve the difficulty. For, first, it imagines intentional species without foundation. Next, it makes them the instrument of material alteration, which is unheard of. Again, it makes them go and return, although they are accidents, unless perhaps it says they are some little bodies, which is more incredible; or unless it says that that return is metaphorical, by reaction, which will at once appear cannot be true in proving the other member, namely, that the difficulty is not solved. Which is evident, first, because those species, whatever they may be, are instruments of the agent from which they flow; they act, therefore, in its power; therefore they cannot exceed its power in acting; how, then, can they intensify it, even if they return to it? Secondly, this action often takes place without any diffusion or action through the medium, as when contrary agents are immediately neighbouring and the power of one is strengthened in itself; for then there are no species which could return to it, because they are neither received in the contrary, as is supposed—for on account of its resistance they are said to return to their principle—nor in the medium, because there is none. Finally, sometimes this action takes place about a subject to which such quality is repugnant, as in well-water; therefore it cannot be through its reflected action.

16. The opinion of others.—It is attacked.—Others, therefore, say¹ that one contrary, surrounded by a stronger one, from the natural appetite of its conservation gathers and unites itself and turns its action into itself in order to protect itself. And Nifo adds, I De Gener., his text 195, in the recognitio, dub. 2, that one contrary per se has the power of acting through some sphere, and, because it is impeded by the opposing contrary from diffusing it outside itself, it turns it into itself and so intensifies itself. But this opinion too is both false and does not solve the difficulty. It is proved, because it already admits not only that like acts on like, but also that the same thing acts on itself according to the same formal quality. Nor does it matter if it be said that this happens on account of the surrounding contrary and as it were from fear of it; for either there is in the quality itself an intrinsic natural power for that action or not; if there is, then from the beginning and always it will effect that action and intensification in itself without the occasion of the contrary, because a natural power naturally executes its whole force without another occasion, provided it is not impeded. But if there is not in the thing a power sufficient for that action, it will not effect it, even if the contrary presses it. A similar argument will be made by inquiring whether that greater intensity is natural to such a thing and quality or not. For if it is natural, it will always have it flowing from its intrinsic nature, nor will it wait for the necessity of protecting itself from the contrary in order to make it. But if it is preternatural, it cannot come from within from the quality itself.

17. And again I shall ask whether that greater intensity, acquired from within on the occasion of the pressing contrary, perseveres in the thing when the contrary is removed before it diminishes it,² or not. For if it perseveres, it is a sign that it is natural, and would from the beginning and per se always have been going to be without the occasion of the contrary agent, if there had been no impediment. But if it does not persevere, then it never could be produced from within; for a perfection which flows from within is not taken away without an extrinsic agent. Finally, it can scarcely be understood what those words signify, that the agent gathers itself and unites itself more, or that it turns its action to itself. For either they signify that it condenses itself and reduces all its parts into a smaller place, and this is easily disproved by the arguments made, applying them proportionally, because either that motion or condensation is natural or not; if it is natural, it will always be present, speaking per se; if it is not natural, it will not take place from within on account of the pressing contrary. Which experience also confirms, for we do not experience in all things which suffer from their contraries motions of this kind; but it would have to take place in all, if it came naturally by virtue of the appetite of protecting itself from the contrary. As for what was added, namely, that the agent turns its action into itself because it is impeded from diffusing it, it has no likelihood, because from the fact that the agent ceases from action on another it does not become capable of action on itself, nor of greater intensity. Otherwise a thing existing in a vacuum would by that very fact intensify itself, because it cannot act on another. Likewise, because that effecting of greater intensity exceeds its proper power; therefore, although the agent is impeded from going forth into action proportioned to it, it cannot for that reason effect in itself an action which surpasses its proper power.

18. Others, therefore, not finding a way to declare this action, deny that there is such action in things, and to the experiences answer that they are apparent, not true; and various causes of such appearances are devised which are fictitious and repugnant to sense; although Galen, bk. III On the Faculties of Simple Medicines, c. 3, is inclined to this opinion.

19. A twofold way of declaring action through antiperistasis.—Why baths and the stomach of an animal are warmer in winter.—The same of well-water.—It must be said, therefore, that a quality is intensified on the occasion of a surrounding contrary in only two ways, namely, either by an extrinsic agent which on that occasion is enclosed and detained there, or, conversely, because on that occasion the extrinsic corrupting agent withdraws, and at once the thing brings itself back from within to its natural state, which demands that greater intensity; and so it comes about that a quality never intensifies itself. The first mode we touched upon in the preceding section, where we said from Aristotle that baths are warmer in winter because the heat in them is enclosed by the colder medium and prevented from breaking out, which we declared of the hot exhalations. Thus too the belly of an animal is warmer in winter, because the animal spirits are retained within, since the coldness of the air constricts the skin and pores, as Galen noted in declaring the cited aphorism of Hippocrates, and Aristotle elegantly, sect. 2 of the Problems, q. 29, where he adduces other examples. And from the same cause (I think) it comes about that in winter the water of a well is warmer, because, namely, some hot exhalations generated in the caverns of the earth are prevented from ascending, the medium being denser and thicker on account of greater coldness.

20. In which experience, however, two things are difficult. One, whence such exhalations are there. The other, how, since they are most subtle, they can act on the water, which is most cold. To the first it must be said that by the power of the sun and of the other heavenly influences such exhalations are generated from the earth, which on account of its density and dryness, which, speaking per se, it has greater in the lower parts, is apt matter for such exhalations to be aroused from it. And perhaps very many of these, generated there in summer time, are afterwards detained there longer for the cause stated above. Those, however, since they are subtler than water, are easily mixed with it while they try to ascend, and so they will easily be able to temper its coldness, at least by continually reacting on it. Perhaps too the air enclosed in the caverns or pores of the earth, since by its nature it is hot, is for the same cause hotter and helps towards that action. The other mode of this action is declared by other examples. The first is of well-water, which in summer time is colder; for the hot exhalations by which it could be heated do not remain there, but ascend more quickly, both because the medium, since it is hotter and rarer, does not impede, and also because at that time those exhalations are subtler on account of the more vehement influence of the sun. And so, the contrary agent being removed, the water becomes colder from within—not colder than its nature demands, but than it was before while it suffered more from its contraries. In this way too it happens that cold water exposed a little to the sun in summer becomes colder; for the extrinsic heat effects in the medium, or in the external surface of the water, or in the vessel which contains it, some rarity; and then, if any hot vapour surrounded the water or was mixed with it, it evaporates more easily, and thence it comes about that the water brings itself back more to its natural state; and perhaps too it is condensed further, not only for the said cause, but also on the occasion of avoiding a vacuum; and from this head too the cold increases. Aristotle may be read, sect. 24 of the Problems, q. 13, and I Meteor., c. 12. In one or other of these two ways, then, all similar experiences can be declared, so that it is never necessary to admit that the same thing intensifies itself according to the same quality; for when that intensification is from within by natural emanation, it is attributed to the generator.

Whether a multitude of agents, or the density of the matter of one, contributes to the intensity of the action

21. The affirmative opinion of some.—In the third argument two difficulties are raised: one is whether a quality existing in a denser subject can intensify in another, rarer one a quality like itself beyond its own grade; or, what is the same, whether several partial agents, or several parts of the same agent, on account of greater application to the same patient like it in quality and equal in grade, can intensify its quality. For many affirm so, as Marsilius, I De Gener., q. 19; and Soto, II Phys., q. 2; and Nifo, I De Generat., his text 195, dub. 2, q. 2. Their reason is that the power of the agent grows not only from the intensity of the form but also from its multitude, Aristotle saying, VIII Phys., text 80, that in greater magnitude there exists greater power; therefore, if that whole power is applied more to the same patient, as happens when the agent is denser, it will also make a greater effect. And it is confirmed by the common example given above of red-hot iron, and of two equal luminous bodies equally applied to the same part of the air. Likewise of equal acts multiplied, which intensify a habit, and of equal drops falling equally, which at length hollow a stone. And it is confirmed secondly, for the air in winter freezes water, because, namely, it intensifies its coldness beyond that grade of coldness which it has in itself; for if it were itself so cold, it too would be condensed and become water.

22. Nor do these authors think this opinion of theirs contrary to the doctrine handed down about the unlikeness required between efficient cause and patient; but they say that, just as like acts on like according to form if it is unlike in grade, so also that which is like in form and grade can act on another like thing if it is unlike in power and potency; and that so it happens in the present case; for something hot as four and very dense, although it does not exceed the air in grade, nor a hand equally hot, exceeds it in power and potency. Because this is not commensurate with intensity alone, as has been said. And it is declared further, because that dense hot thing has the power of producing in another the whole form which it has in itself; since, therefore, in the rarer patient it cannot multiply it on account of the latter's incapacity, it increases it intensively.

23. The reported opinion is rejected.—Resolution of the question.—This opinion I judge false and contrary to the principle laid down, which is to be taken in this sense, namely, that nothing can act on another thing like itself according to that form in which they are alike, nor add to it perfection or intensity, if they are supposed to be perfectly alike, that is, not only in species but also in the grade of intensity; which Aristotle in the cited place of De Generat. says, if they are wholly alike. Wherefore to the argument made it must be said that a multitude of form with equal intensity, whether in one very dense agent or in many however applied, does not suffice to intensify in another a like form beyond that grade which such a form has in the agent. This is the more common opinion, which Paul of Venice holds, in the Summa on Generation, c. 23; Albert of Saxony, I De Generat., q. 15; and Astudillo, q. 21; and excellently Victoria, in the relectio On the Increase of Charity.

24. The a priori reason has already been touched upon, because the agent by its action intends to assimilate the patient to itself, and this end being attained, its action ceases; but if the patient has been made like in form and grade, it is already perfectly like; therefore the action does not proceed further. Nor can it be said that perfect likeness has not yet been made because the patient has not attained so great a multitude of form as is in the agent: both because the multitude or fewness of form does not pertain to the notion of the form or quality itself, but comes from the subject or quantity, and therefore it is not unlikeness in form but inequality in quantity—for one white thing will not be called unlike two white things because it is not many as they are, but will be called unequal; but through action such equality is not intended, but likeness in form; and also because such likeness, or rather equality, is impossible, the capacity of the rare or dense subject being supposed, or, what is the same, it being supposed that the patient is one and the agents many. Nor is it true that that inequality can be compensated by greater intensity, both because they are quantities or perfections of diverse notions, and also because rather through that greater intensity a new unlikeness in grade would be made, the same inequality in the multitude of form remaining.

25. The second reason is that in a remiss form, however multiplied in many and differing subjects, or in many parts of the same subject, there is not sufficient power to effect greater intensity in a like form; therefore. The antecedent is evident, because, in the first place, such power is not there formally, since such intensity is not formally in that form. For I suppose that intensity is not an aggregation of several like grades in the same part of the subject, but a proper and per se increase of the same quality in the same part of the subject; which increase, for example as eight, would not exist even if two heats as four were placed in the same part of the subject, of which I shall speak below in its place; this perfection, therefore, can much less be formally in a multitude of remiss form existing in many subjects or parts of a subject. Nor is it there eminently, since that form according to species is of the same notion, and according to grade is of an inferior notion in the single parts of the subject, and consequently in all taken together. For in many things of the same notion there is not a more eminent power than in the single ones, since eminence of power demands a form or nature of a superior notion. Nor can it be said that that intensity is virtually in that form on account of its multitude, because virtual containment, as it is distinguished from eminential, is attributed only to instrumental power; but in this way that intensity cannot be attributed to a multitude of form of inferior intensity and of the same notion, both because such a form, while it acts what is like itself, behaves not so much as an instrument as a proper principle of acting, as was said above, and also because no principal agent can be assigned in whose power it may be said to effect that effect; indeed that multitude of form per se was not instituted to be the instrument of any action, but is as it were a certain aggregation of instruments of the same notion.

26. Absurdities from the opposite opinion.—Thirdly, I argue from the drawbacks, because from the opposite opinion it follows, first, that three things hot as four could make one another supremely hot, if two joined together intensified the heat of the third up to the fifth grade, and that again rendered the others like itself, and so they proceeded up to the highest. Secondly, it similarly follows that water hot as four according to every part could render itself hotter in any grade whatever; for two extreme parts, for example, will effect in the intermediate one and intensify its heat, and that again will effect in the extreme parts, and so the action will proceed up to the highest. These and similar things, however, are plainly false and against experience. Thirdly, it follows that a habit is intensified by remiss acts, so as to incline to a more intense act, which too is false, as I suppose.

27. In order to answer the foundation of the contrary opinion, it must be noted, first, that it is one thing for the power of acting to grow from the multitude of form, another for it to grow as to the power of producing an effect more perfect intensively; for the former is more general, and from it the authors of that opinion do not rightly gather the latter. The power of acting, then, is increased in that way not intensively but extensively, and therefore it is not increased so as to be able to produce a more intense effect than is the form itself which is the notion of acting, but so that it can effect its adequate effect more easily, more quickly, more strongly and at a greater distance, other things being equal. Hence it can be said to be increased as to the mode of making, not as to the thing which it can make. And similarly, when density of the parts of the subject is joined to the multitude of form, it helps much towards this mode of action, because that whole multitude of form is better applied to the patient, and therefore it conduces to more prompt action; yet by itself alone it cannot conduce to a better effect than is contained in the power of the form, because that application is only a condition which per se does not conduce to acting, except power being supposed.

28. Secondly, it must be observed that the discourse is of a multitude of form which is wholly equal in essence and grade to the form of the patient; for if it happens that the quality of the agent is as to essence and species of another notion from that which is made in the patient, and contains it eminently, although in its own order it were remiss, it can be the principle of effecting the inferior quality intense in its grades, as was touched upon above; for that superior quality in any grade whatever, by reason of its essence, could eminently contain the whole latitude of the inferior quality. Nor then would like act on like, even if a quality, for example as one, intensified a quality as one, because they would be of diverse notions, and that would rather be a certain proportion than proper likeness. Next, it can also happen that a multitude of form conduces to a more intense effect when the effect does not equal the intensity of the form of the agent; as, for example, when one lamp illuminates the air, it does not produce in it so intense a light as it has in itself, and therefore it can rightly happen that two lamps taken together, and of equal intensity between themselves, produce a more intense light in the air than either could by itself; for then the reasons given cease, because the patient has never been made perfectly like the agent; since, therefore, in the agent there is not only a greater multitude of form but also a more intense form, there can be in it power to intensify the effect. Hence in any one of those agents by itself there will be a form productive of that whole intensity; that one agent by itself alone did not produce all of it could come either from the indisposition of the patient, or from distance, or from another similar cause. And then a multitude of intense form can excellently contribute to producing a more intense effect, which yet does not exceed the intensity of the cause.

29. Whether two like or unequal agents help each other in action.—The greater difficulty is, if two unequally intense agents concurred together, whether they could help each other to produce a more intense effect, which, although it does not absolutely exceed the whole intensity of the cause, yet exceeds the intensity of the other partial agent having a less intense form; so that, although a remiss quality, however great in multitude, cannot per se intensify a quality like it in grade, yet in partnership with a more intense quality it can help and cooperate towards intensification. For then too the reasons given seem to cease; for in such a total agent there is absolutely a more intense form and power sufficient for that effect, and the lower grades of quality conjoined to the higher can concur to any grades whatever of another like quality; as, for example, when something hot as eight intensifies heat as four, it does not concur to the fifth grade, for example, only through the fifth of its heat or through the higher ones, but through its whole heat; just as conversely, when it makes the first grade, it does not effect it through the first, but through its whole heat. A sign of which is that for effecting the first or the fifth grade what is hot as eight has greater power than what is hot as five or as one, other things being equal; for it will both overcome greater resistance and act more quickly; therefore it is a sign that it does not act only through the like grade, with the others related concomitantly and as it were per accidens to that action, but that they truly concur to it. And the reason is that, in order that all help and concur, it is enough that in all and each there be the essence of heat, although there is not in the single grades that peculiar likeness which is between grades of wholly the same notion; for it is enough that that likeness be in the whole form, which is the principle of acting. Thus, then, several remiss forms too, conjoined to a more intense one, will be able to concur with it to producing a more intense effect. This, then, is probable, nor do the reasons given so militate against it, as is easily evident from what has been said; and it can contribute to saving some experiences, as was touched upon above and as we shall see at once.

30. It is not, however, free from all difficulty; for if a remiss form, conjoined to a more intense one, acts towards the intensification of a form like itself, why will it not rather act towards the intensification of itself? Likewise, because otherwise something hot as eight, equally neighbouring two things hot as four, would act with one and through it towards the intensification of the other, and conversely. It could be answered, however, that it comes from a peculiar disposition of the patient or of the partial agent that one remiss partial agent cooperates more with the more intense agent to intensify a like form in another subject than in itself, or than another like thing, as will more easily be established from what is to be said. This, then, is probable, of which more below.

31. How red-hot iron generates fire.—From these, then, the foundation of the contrary opinion is sufficiently disposed of. To the first experience brought by us, however, of the red-hot iron, the common consent and reply of all philosophers is that there is some fire enclosed in its pores, although it is hidden from us; from which fire enclosed in the pores of the red-hot iron comes that greater intensity which we easily experience by the senses, although the vehemence and quickness of the action comes from the partnership of the iron and its density. A sign, however, that there is some fire there enclosed and contained (as we said just now) in the pores of the iron can be taken from the brightness which always comes from fire, as Plato said in the Timaeus. Likewise this very thing can be shown by a reason by no means to be despised, because iron is not without pores, in which there is commonly air; therefore, since vehement heating has intervened, it will be turned into fire by the force and efficacy of so intense and vehement a heating. And finally, never does so vehement a heating take place in any matter or subject capable of such heating without some exhalations being separated from it and inflamed or turned into fire. Others answer for a far different reason, namely, that there is in the iron the supreme heat that can be, and this without the form of fire on account of other dispositions repugnant to fire and conserving there the form of iron. But it is hard to believe that those dispositions which connaturally exist in iron as in a subject proportioned and connatural to them do not also impede so great an intensity of heat, since they are repugnant from the nature of the thing. I intimated another reply above, that in dry and disposed matter fire can be generated without preceding supreme heating, which can easily be defended, and this being posited, it does not follow that there is supreme heat in the iron. The first reply, however, is sufficient.

32. Whether remiss acts increase a habit.—To the experience adduced about remiss acts, it is answered that it rather proves the opposite, because according to the common opinion they do not intensify or increase a habit; although this requires a longer exposition, which we shall give more ex professo in its place. To the other, about falling drops, it is answered that each does something, because they gradually dispose the subject, which they render somewhat softer; otherwise, if the subject remained equally indisposed, the second could do nothing more than the first, nor the hundredth than the third; yet each acts on an unlike patient; for of itself, for example, it was dry, and at the beginning it begins to be moistened according to the proportion and power of the falling drop; but because the later ones find the patient more disposed, they do more; none, however, acts beyond its proper intensity and power. To the third, about frost, it is first denied that the air cools the water more than it is itself cold; but at most it can wholly prevent it from being heated by an extrinsic agent, and then the water itself brings itself back to the supreme coldness which by its nature it can have. But if that coldness suffices for congelation, then it does not come from the air; but if it does not suffice (as indeed it seems not to suffice, otherwise water existing in its natural state would always be frozen), then too another cause of that congelation besides the air will have to be sought, because the air was said only to cool. I think, however, that congelation comes from the diminution of the moisture of the water, and hence from some heavenly drying influence; for that dryness, so affected and tempered with such density and coldness of the matter, accomplishes congelation; no quality, therefore, intervenes there which is intensified by a more remiss quality of the same notion.

On reflected action

33. The other doubt raised in the same argument concerned reflected action, in which some confess that a remiss form can intensify itself, let alone one like itself. Which opinion, taken so absolutely and universally, we rejected above, and we shall at once add something against it again. Others say that through reflection the solar rays, for example, are multiplied about the same part of the medium; for because of themselves (they say) they could pass further, obtaining a greater sphere, therefore, when they meet a body which impedes their diffusion, they return to the same patient from which they are reverberated, and so reflection takes place. But unless these things are said by metaphor, they are plainly false and openly contrary to reason; for rays are imagined to be certain little bodies which arise from the sun, which was the view of Democritus about every agent, rejected by Aristotle and all philosophers, as St. Thomas generally noted, I, q. 115, a. 1, and specially of light, q. 67, a. 2.

34. The first way of explaining the question is disproved.—It can be understood in two ways, then, that action on the medium is more intense on account of reflection. First, because, while the principal agent operates in a smaller sphere, it acts more intensely in its parts than if its action were diffused to a greater sphere; which principle per se indeed appears probable, for finite power applied to more things is less in each; therefore, conversely, gathered to fewer, it will act more strongly in each; therefore it will also act more intensely, yet within the latitude of its power and intensity. Thus, then, fire heating this hall, although it could heat at once a much greater sphere, yet because its action is held within the bounds of the hall, makes a more intense heat in this air than it would otherwise make; and the same holds proportionally of the sun illuminating. Although, however, the intensity is then said to be greater on account of reflection, yet in truth that reflection, so expounded, on the part of the body in which it takes place, is only an impediment to the action's proceeding further; but on the part of the principal agent there is more efficacious action and greater application of its power.

35. But this way of explaining reflection, and action through it, although it is probable in what it affirms, does not seem, however, to suffice by itself to save all that experience shows in reflection of this kind. First, indeed, because, if the body in which the reflection takes place served only as an impediment of diffusion, by reason of which the power of the first agent, as it were united to a smaller sphere, acts more strongly on it, any body placed at the same point and equally impeding the extension of the sphere would make equal reflection, for it would give wholly equal occasion to the first agent to intensify its action more strongly and (so to speak) double its strength; but the consequent is openly against experience; for a black thing, for example, other things being equal, does not make equal reflection of light as a white thing; nor a white thing equal to a mirror. Secondly, because, if reflection took place only in that way, it ought to take place in equal proportion through the whole sphere; for that stronger action or application of power takes place in equal proportion to that whole. But the consequent is against manifest experience, for stronger reflection takes place in the parts nearer to the body from which the reflection takes place, as is sufficiently established per se.

36. The body which reflects the action truly acts on that against which it reflects.—Wherefore it seems necessarily to be said that in this said reflection there intervenes proper efficiency of that body in which the reflection takes place; for it receives from the first agent an active form or quality, and, affected with that, acts again on the patient nearest to it, which is the very medium through which the first action of the agent came as far as that body. And therefore that first action of the agent is called direct, but the other is called reflected. This mode, however, is not proved otherwise than from a sufficient enumeration, and because per se it is probable and involves no repugnance, since it often happens that one thing through a form received from without acts again, as hot water through heat. It is not, however, without its difficulties; for in the first place it can be asked, since the medium receives the same quality from the first agent, why it does not rather itself act on the other, from which the reflection is said to take place, than suffer from it. It is answered that this comes from a peculiar disposition or condition of such a body and quality; for light, for example, does not seem per se active unless it is received in a dense and polished body; or at least it is not equally active, as experience teaches; for this is why the moon illuminated by the sun illuminates more than other parts of the heaven, because it is so lucid as to be also dense. Since, therefore, the reflection of light always takes place in a dense body towards a rare medium, therefore that action is rather from such a body than from another. Something similar is found in the reflection of heat; for it commonly takes place from a denser body, which acts more strongly, as was said above, on account of the multitude of matter.

37. A doubt is satisfied.—But then a second difficulty arises, because hence it follows either that the first agent heats or illuminates the distant thing more intensely than the near, on account of its disposition, or that that distant thing in which the reflection takes place intensifies a like quality in the medium only on account of the greater multitude of matter, although in it the quality is either less intense or at most equal; but both are repugnant to what was said above. This is the argument by which those are chiefly moved who say that in reflected action what is like in grade is intensified by what is like, or the same by itself. But this was partly attacked above, and moreover it can easily be refuted, because reflected action is true action and cannot take place without sufficient power, and has nothing special except the denomination, because it is bent towards the agent from which the form is directly received from which the reflected action is. And therefore someone could answer that this reflection never takes place except either through a quality of a diverse notion or with some like quality helping; as, for example, when a mirror heats through light by reflected action, then the reflection is said to take place through a quality of a diverse notion, and the touched difficulty easily ceases, as was said above; because, although the light is not more intense in the mirror than in the air, it can heat more intensely, because it is a quality of a superior notion, and from elsewhere it is helped by the density of the subject and the multitude of form more applied. But when reflection takes place between lights themselves, the said reply has no place; and therefore there will not then be lacking one who denies that there is in reality such reflected action by which the light of the medium is made greater, but that it so appears because that polished or white body moves the sight more vehemently. But this does not appear credible, because we experience that the air itself shines more clearly when reflection takes place, and objects placed in it are better seen. It could also be said that the light in the medium is not intensified, but a new one is made by the body through reflection; and that it is not unfitting that two lights be together in the same part of the air. Just as, when reflection takes place in a mirror, it is probable that a new visible species of the same object is caused in the medium by reflection. But this multiplication of lights, although it pleases the perspectivists, has not been received by the philosophers, nor is it consonant with what was said above about the individuation of accidents. And therefore it could otherwise be said that the light received in a dense body is of a diverse notion from that which is received in the air, which is hard to believe. Or it could also be said that it is helped by some quality of the subject; but all these and other things which can easily be devised would be affirmed without foundation, rather to flee the difficulty than to resolve it.

38. Wherefore it seems necessarily to be admitted one of the consequences stated, provided it is not understood that a remiss quality by itself alone intensifies what is like itself, but in the power and with the partnership of the principal agent; for this was declared above to be probable. If, then, we say that the sun, for example, on account of the greater capacity of the subject, illuminates a distant mirror more intensely than the intermediate air, the medium itself helping as instrument or partial agent, then it is easy to understand that the mirror so illuminated acts again on the air neighbouring it and intensifies the light; for it is not unfitting that in the same quality some grades be made by one agent and others by another, when they act by diverse actions and not equally firstly, but with some order, as happens here. But if we say that in direct action the remote mirror is not more intensely illuminated than the intermediate air, then it must be said that, because the mirror is more apt for acting through received light than the air, as soon as it is illuminated it is virtually conjoined to the first agent and helps it and is helped by it to intensify the light of the air. And so these two ways of speaking can be probably defended, although, all things weighed, between these two the first seems easier and to declare reflected action better and to avoid the difficulties.

On reaction

39. In the fourth argument the difficulty about reaction is raised, and how in it the greater proportion necessary for effective causality is saved. But this difficulty is treated most broadly in bk. I De Gener., and depends chiefly on understanding the difference which is between the power of acting and of resisting, which we shall hand down below in treating of power. Now, therefore, it is briefly said that formally to resist something is not to act on it; for a thing can sometimes resist even if it does nothing on another. From which it comes about that for acting it is not necessary that the power of acting of one be greater than the power of acting of the other, but per se it is only required that the action of the one overcome the resistance of the other. Hence, then, it comes about that the patient reacts on its agent even if it suffers from it more vehemently, because, although it is surpassed in activity, it can nevertheless by its activity somewhat overcome the resistance of the other; and so it does not act on it inasmuch as it is greater than or equal to it, but inasmuch as it is in some way inferior. But these things will be better understood when the notions of active and resistive power, and their proportions, have been explained, which we shall carry out below. The last argument was solved above.