In De ente et essentia D. Thomae Aquinatis commentaria

Whether intelligences can be known quidditatively by us in this life.

Concerning this point it is questioned whether intelligences can be known quidditatively by us in this life, etc.

In this question seven things are to be done: first I shall explain the title and intention of the question; second, the opinion of Averroes will be brought forward; third, it will be attacked; fourth, his reasons will be answered; fifth, the opinion of St. Thomas will be explained; sixth, the reasons of John of Jandun against St. Thomas will be brought forward; seventh, they will be answered.

Regarding the first, note that knowing a quiddity, or knowledge of a quiddity, is one thing, and quidditative knowledge, or knowing quidditatively, is another. For whoever knows some essential predicate of a lion knows the lion’s quiddity. But only he knows it quidditatively who knows all its quidditative predicates down to the ultimate difference, etc. Since we know that intelligences are substances and intellectual, etc., it is clear that we know their quiddities; hence this is not in doubt. The question is whether we can know them quidditatively, that is, penetrate as far as their ultimate differences. Although this question has many opinions, as is clear in III On the Soul, commentary 36, since here the dispute is only with Scotists and Averroists, and the Scotist opinion does not differ in its conclusion, as is clear in I Sentences, distinction 3, we have to dispute with Averroes alone. So much for the first.

Regarding the second, Averroes in III On the Soul, commentary 36, presupposing his fiction in commentary 5, holds that the possible intellect, as appropriated to us, after acquiring all the speculative intelligibles, and thereby being joined to the agent intellect as to its form, will through it understand separate substances; and consequently we, for whom the agent intellect will thereby become a form, just as the possible intellect is now, will then understand separate substances through the agent intellect, just as now we understand material things through the possible intellect.

He proves his intention by two arguments. The first rests on two propositions. The first is: the intellect and the first speculative intelligibles are related as form and matter. It is proved thus: things having one and the same operation, such that the operation of one is communicated to the other, are related as agent and instrument, or as form and matter. But the operation of the agent intellect and of the first speculative intelligibles is one and the same, such that the operation of the agent intellect, namely, making intelligibles in act, is communicated to the first speculative intelligibles. Therefore the agent intellect and the first speculative intelligibles are related as agent and instrument, or as form and matter. The minor is clear, because the intellect in habit can not only understand but make intellectual conclusions that are intelligible in potency into intelligibles in act; in both respects we experience that it is in our power to understand and to make conclusions actually understood through the first intelligibles, which by the sole light of the agent intellect become intelligibles in act. is communicated to the first speculative intelligibles. Therefore the agent intellect and the first speculative intelligibles are related as agent and instrument, or as form and matter. The minor is clear, because the intellect in habit can not only understand but make intellectual conclusions that are intelligible in potency into intelligibles in act; in both respects we experience that it is in our power to understand and to make conclusions actually understood through the first intelligibles, which by the sole light of the agent intellect become intelligibles in act. In the major, however, it is expressly said “such that the operation of one is communicated to the other,” because several people pulling a ship cooperate in the same operation, yet not as matter and form, nor as agent and instrument, since neither takes on the proper operation of the other. But that which communicates its operation to another by cooperating in the same thing is related to it as a principal agent to an instrument, as a carpenter communicates the making of a chair to a saw; or as form to matter, as heat communicates the heating of water, etc. Although either part of the disjunction concluded is true, since the first is more evident and less relevant to the purpose, the Commentator explains the second part: namely, that the first speculative intelligibles and the agent intellect are related as matter and form. He does this by explaining that the agent intellect, and not only the first but all speculative intelligibles, are related as form and matter.

He manifests this as follows: whenever there is something receptive of two things ordered among themselves, what is more perfect and more formal is as form, while what is less perfect and less formal has the character of matter. But the possible intellect is receptive of speculative intelligibles and of the agent intellect, which are ordered among themselves, so that the agent intellect is more perfect and formal than the speculative intelligibles. Therefore the agent intellect and the speculative intelligibles are related as form and matter. The major says “ordered among themselves,” because otherwise the proposition would not be true, as is clear of the whiteness and sweetness of milk, neither of which is the form of the other. For when things are ordered, the proposition is necessarily verified, as when air receives color and odor. The minor is clear from the fact that the intelligible is received in the one understanding. But the possible intellect understands both the agent intellect and the speculative intelligibles, etc.; thus the first proposition is clear.

The second proposition is: the possible intellect appropriated to us sometimes receives the speculative intelligibles and the agent intellect in pure potency; sometimes partly in act and partly in potency; sometimes wholly in act. This proposition, as regards the speculative intelligibles, is most clear: the intellect of an infant is in pure potency, like a blank tablet on which nothing has been depicted; afterwards it receives knowledge of the first principles; then it successively acquires knowledge of many conclusions. Thus in one respect it is in act, for example with respect to principles, and in another in potency, for example with respect to conclusions; finally, having acquired all conclusions, it is wholly and in every respect in act, with respect both to principles and conclusions. If you join the first proposition to these, this second proposition will become clear to you with respect to its second part. For if the agent intellect is the form of the speculative intelligibles, the proportion of its union with the agent intellect will be the same as that between the possible intellect and the speculative intelligibles, in this respect: if it is wholly united to one, it will be wholly united to the other; and if partly united to one, it will be partly united to the other.

With these premises, Averroes’ first argument is formed thus: whatever is moved toward acquiring something as a form can, once it has perfectly acquired it, operate with the proper operation of that form. But the possible intellect appropriated to us is moved toward acquiring the agent intellect as a form. Therefore, once it has acquired it, it can operate with its proper operation. But the proper operation of the agent intellect is to understand separate substances quidditatively. Therefore the possible intellect will be able through it to understand separate substances; and since the possible intellect’s new activity denominates us, consequently we understand substances through the agent intellect, etc. The major is clear by example: when water is moved by the form of heat, once it has acquired it, it can heat; and the same appears in all cases. The minor is proved in two ways. First, from the two foregoing propositions: whenever something is moved to receive two things ordered among themselves, it is moved to the more formal and perfect one as to a form, by the first proposition. But the possible intellect is moved to the speculative intelligibles and to the agent intellect, because it is sometimes in pure potency and sometimes partly in act and partly in potency, according to the second proposition; these are ordered among themselves because the agent intellect is received through the speculative intelligibles, and the agent intellect is more formal and perfect. Therefore the possible intellect is moved to acquire the agent intellect as a form.

Second, the minor is proved thus: the possible intellect is moved to acquire the agent intellect as an end; therefore, as a form. The antecedent is clear from the fact that the agent intellect itself is the efficient cause of that movement by which the possible intellect is moved toward it; for among things separate from matter, the efficient cause and the end of motion are the same, as is stated in commentary 36 of XII Metaphysics. The consequence is clear from II Physics, text 70, where it is said that end, motion, and form are the same; Averroes touches on this proof in XII Metaphysics, at the end of commentary 38.

Averroes’ second argument is set out in III Metaphysics, commentary 1. If intelligences could not be known by us, nature would have acted uselessly; the consequent is false. The consequence is proved because nature would have made what is naturally intelligible in itself not intelligible by another, as if it had made the sun not comprehended by any sight. Since St. Thomas judges this consequence and its proof ridiculous, because what cannot attain its end is useless, and the end of intelligences is not to be understood by us—for even if being understood were their end, it is enough for their intelligibility that they be understood by themselves; it does not follow that, since they are not understood by the human intellect, they are understood by no intellect, just as it does not follow that, since the sun is not seen by an owl, it is seen by no sight—

John of Jandun therefore proves that consequence in two ways in III On the Soul. First, he says that the Commentator does not suppose that the end of separate substances is to be understood by us; rather, it is supposed that intelligences are of themselves intelligible to our intellect, since they are contained under its first object, namely being. Then it rightly follows: intelligences are naturally knowable by us in themselves; therefore our intellect is naturally born to understand them. For a natural passive power, such as the intellect, must correspond to a natural active power, such as intelligence; otherwise an active power would be useless in nature. Second, the same consequence is derived from this: although the primary end of intelligences is not to be understood by our intellect, it is nevertheless their secondary end. For they act primarily for themselves and secondarily for other things, as is said in II On the Heavens, commentary 21; therefore it follows that intelligences, at least with respect to their secondary end, would be useless, and thus nature would have made something useless. Hence, he says, the Commentator’s consequence is close to propositions known per se and is not ridiculous. A third derivation can still be made from the Commentator’s statements in III On the Soul, commentary 36, where, examining Themistius’ argument, he says that if our intellect is immaterial, this consequence holds: our intellect understands sensible things made immaterial; therefore it understands things immaterial in themselves. This statement is based on Aristotle’s word in III On the Soul, text 7, saying that the intellect, after apprehending an excellent intelligible, is strengthened to understand something higher. From this it follows in the present case that immateriality is a sufficient cause for a cognitive power to be able to understand separate substances. Thus the consequence is proved: intelligences are not knowable by our intellect; therefore they are knowable by no other; therefore it is useless for them to be knowable, just as the sun would be uselessly visible if it could be seen by no one. The first consequence holds because, if immateriality does not give our intellect the power to understand them, it will give this power to none, since it has already been shown that immateriality is a sufficient cause of it. Thus, because the sensory power is a sufficient cause of the sense of touch, if it did not produce touch in one species of animal, it would produce it in none. The second consequence is clear by the example. Therefore every intellect can know separate substances from its immate-

With respect to the third, the opinion is attacked in two ways. First it is proved that the posited continuation does not bring the possible intellect appropriated to us to understand separate substances: that which is joined to the agent intellect only as the form of speculative intelligibles cannot through it understand separate substances quidditatively. But the possible intellect appropriated to us is joined to the agent intellect only as the form of speculative intelligibles. Therefore the possible intellect appropriated to us cannot through such continuation understand separate substances quidditatively.

The major is proved by supposing that the agent intellect has proportions of different orders to higher and lower things, namely immaterial substances and speculative intelligibles. For it is related to higher things as contemplative, not as their form; to lower things, however, as productive and as form. Given this, the force of the major is clear.

Whenever one thing has a proportion of different order to different things, what is joined to it according as it has a proportion to lower things is not thereby joined to it according as it has a proportion to higher things. For a manifest fallacy of accident is committed by concluding one thing from another. Therefore what is joined to the agent intellect as the form of speculative intelligibles is not thereby joined to it as the contemplative intellect of immaterial substances. The minor is had from the Commentator’s statements, since he posits no other way in the present matter by which the possible intellect is joined to the agent except through speculative intelligibles. Hence he says that when it is in pure potency with respect to speculative intelligibles, it is also in pure potency with respect to the agent intellect; when it is partly in act and partly in potency with respect to them, it is likewise with respect to this; and when it is wholly in act according to the speculative intelligibles, it will be wholly joined to the agent intellect.

Second, it is proved that even if such continuation brought the possible intellect to this, it can never bring us to it, and I argue thus: what is joined to the agent intellect only as colored is joined to light, and to the possible intellect only as colored is joined to sight, cannot be denominated as operating with the proper operation of light or sight, that is, of the agent or possible intellect. But a man imagining has this sort of continuation with these intellects. Therefore he cannot be denominated as making intelligibles and understanding immaterial substances, which are operations of the agent intellect, nor as understanding sensible things, which is the operation of the possible intellect. The minor is evident from the terms: it cannot truly be said that a colored thing illuminates or sees. The minor is also clear from III On the Soul, texts 18 and 30. Nor does it at all obstruct the likeness given that a man by his own act of the cogitative power spiritualizes phantasms. A colored thing does not spiritualize colors. For if we imagine a colored thing unable in itself to be presented either to the eye or to light, but spiritualized only in a mirror, whose proper operation would spiritualize the species of the colored thing in itself, the likeness would run on all four feet; yet such a mirror, presented to light and sight, could not truly be called illuminating or seeing. This argument appears to me demonstrative; and on another occasion, if God grants us life, we shall show its efficacy more fully. So much for the third.

Regarding the fourth: to Averroes’ first argument it is said that the major is universally false if it is held as it must be held in order to conclude the intended point. It must be held universally not only with respect to the subject but also with respect to the predicate, as follows: everything moved to acquire some form, once that form has been perfectly acquired, can operate with every operation proper to that form; otherwise it would not conclude. But this is clearly false, since it is enough that what has acquired a form participate in some operation of that form, namely the operation belonging to the form according to its relation to the receptive subject. The reason was assigned in the first argument against Averroes: a thing joined to a form having different proportions to lower and higher things need not, because it is perfectly joined to it with respect to the lower, be joined to it with respect to the higher. Hence, from the fact that the possible intellect acquired the agent intellect as a form, it follows that it can operate with the operation of the agent intellect as the form of speculative intelligibles, since it is acquired in this respect, namely to form intelligibles in act and extend itself to all things to which the agent intellect extends itself as productive; but it does not follow that it can understand everything to which the agent intellect is related as contemplative.

To the second argument the consequence is denied. To the first proof it is said that a fallacy of consequent is committed, affirmatively from a superior to its inferior. Even granted that intelligences are knowable by our intellect because they are contained under its first object, it does not follow that they are intelligible by us quidditatively. For not everything contained under being is quidditatively intelligible by us, since being, although extensively the adequate object of our intellect, is not adequate by mutual adequation intensively. That is to say, although every being can be understood by us, not every being can be penetrated by our intellect down to its ultimate differences. In this way the quiddity of a material thing is the adequate object of our intellect, namely by intensive adequation; our intellect is naturally born to understand quidditatively that alone and the whole of it.

The same answer is given to the second way of deriving the consequence: even if it is granted that being understood by us is a secondary end of intelligences, it does not follow that being understood quidditatively by us is their secondary end; indeed, this is impossible.

Likewise, regarding the third way, it is said that although immateriality is a sufficient cause for a cognitive power to be able to understand separate substances, it does not follow that from immateriality it has the ability to know them quidditatively.

The authority of Aristotle that was brought forward does not obstruct the argument when correctly understood. It must be noted that, with respect to an excellent sensible, the sense has two effects: it does not perfectly know it, and it suffers a corruptive passion from it. With respect to an excellent intelligible, however, the intellect has only the first: it does not perfectly understand it, for it is immune from passion. The reason is that the second follows matter, whose act is the sensory power, but not the intellectual power; the first follows the disproportion of the power to the object, which is preserved in an immaterial power just as in a material one. Just as an owl, by its species, has sight disproportionate to bright light, so man by his nature has an intellect disproportionate to a bright separated intelligible, that is, to one really separate from matter. Thus intellect and sense agree in the first respect but differ in the second.

From this difference Aristotle says there arises the fact that sense is weakened after sensing an excellent sensible; the intellect, however, is not altered after understanding an excellent intelligible, but can understand other things more, which must be understood according to the mode possible to it. From this it is not permitted to infer that it can know immaterial substances quidditatively; rather, it does not follow from its alteration that it cannot comprehend them, which we freely grant. For man has a discursive intellect, which arises in the shadow of intelligence, according to Isaac; and therefore he is naturally proportioned to behold not a pure and clear intelligible, but one overshadowed by matter, such as the quiddity abstractable from sensible things. So much for the fourth.

Regarding the fifth, I set down the opinion of St. Thomas, which I take from I, question 88, III Against the Gentiles, chapter 45, and II Metaphysics. He maintains this conclusion: the human soul joined to the body cannot know immaterial substances quidditatively. This is presently proved in two ways. First: an intellect existing in potency only for receiving intelligibles abstracted by the agent intellect cannot understand immaterial substances quidditatively; the human intellect is of this kind; therefore. The major is clear from the terms, for the opposite of the predicate entails the opposite of the subject. What can understand separate substances quidditatively is not merely in potency to receive abstractions from the agent intellect, since separate substances are not abstracted from matter through the operation of the agent intellect. The minor is gathered from Aristotle, III On the Soul, text 17, where it is said that the agent intellect can make all things that the possible intellect can become.

Second: no sensible effect can lead to quidditative knowledge of separate substances; therefore the human intellect joined to the body cannot know them quidditatively. The consequence holds because nothing is in the intellect unless it was first in the sense. The antecedent is proved from the fact that an effect can lead to quidditative knowledge of its cause in two ways. Either by way of likeness, as when a univocal effect is known, we know its cause quidditatively because they are of the same nature; and in this way it is clear that no sensible thing can lead to the natures of immaterial substances, since they differ not only in species but in genus. Or an effect leads to quidditative knowledge of its cause not by way of likeness, but by showing the whole power of its cause. Thus understanding shows the whole power of the intellectual soul, and therefore from such an operation we proceed to knowledge of its quiddity. Nor can sensible things lead us to quidditative knowledge of intelligences in this way. For no particular effect equals the whole power of a universal cause; and every sensible thing is a particular effect, as the material conditions of each show. Therefore through no sensible thing can we arrive at quidditative knowledge of immaterial substances, which are the most universal causes, etc.

Regarding the sixth, the aforementioned John of Jandun argues in many ways against this determination in III On the Soul. First against the phrase in the conclusion, “joined to the body”: no form is prevented from its noblest operation because of its union with its proper matter. But understanding the quiddities of separate substances is the noblest operation of the human soul, as is clear in I and X Ethics. The human body is its proper matter. Therefore the human soul is not prevented by its union with the body from contemplating immaterial substances.

Furthermore, for the same conclusion: the human soul is either naturally born to understand separate substances through its substance, or through an infused species, or through a species caused from a phantasm. If through its substance, since its substance is not impeded by union with the body, it will be able to understand them. If through a species taken from a phantasm, union with the body will help. If through an infused species, one asks how union with the body impedes or does not permit such infusion. For this does not seem reasonable in any way, because the generation of one species is not impeded by a body unless the body has a disposition contrary to the disposition required for its generation. For example, because color requires transparency in air in order to be received in it, no body will impede the generation of the species of color unless it has opacity contrary to transparency. But the human body has no disposition contrary to the disposition required for the reception of an intelligible species to be infused, as is clear; therefore.

The argument is confirmed thus: the unqualified good of a nature is not impeded because of the unqualified good of that same nature. For what impedes the unqualified good of a nature is an unqualified evil for it. But understanding the quiddities of immaterial substances is an unqualified good of the human soul. Therefore it is not impeded by union with the body, since this too is an unqualified good for it.

Third, an argument is made against the conclusion itself from the words of St. Thomas as follows. They say that we know the existence of the intelligences, not their quiddities: either existence is the same as quiddity, or different. If different, then both fall within our cognition; for whoever knows the diversity of some things knows the extremes of that diversity, as is said in On the Soul II, text 36. If the same, then, once one is known, the other is also known.

If it is said that we know those quiddities, but not perfectly, there is an objection. First, because this conflicts with two statements of the Thomists. The first is that we do not understand the quiddities of separated substances. The second is that we know their existence, not their quiddities. From the first the argument is: man does not understand separated quiddities; therefore he does not understand them at all. The inference holds by the place from the whole in mode to its negative part. From the second the argument is: the cognition that is denied of the quiddity is affirmed of existence; but existence is known by us only imperfectly; therefore they intend to deny even imperfect cognition of quiddities. For if we know both imperfectly, why is one rather denied to be known, or the other affirmed?

Second, it is proved that the response is false in itself as follows. If we know those quiddities imperfectly, either this is because we do not know them as perfectly as they are known by themselves—and this is not so, because it would be ridiculous to cast this into doubt—or because we do not know them with the perfection due to us according to our nature—and this is voluntary, for it can be compelled by no reason. Union with the body cannot impede this, as has been proved. This concerns the sixth point.

Regarding the seventh point, as a preliminary to the response to these arguments, it should be noted that according to the teaching of St. Thomas in Summa I, questions 88 and 89, the difference between the cognition of the conjoined and separated soul is this: just as the conjoined soul has its mode of existence by involving the body, so it has its mode of understanding by turning toward phantasms. Thus, from the conformity of its mode of operation to its mode of existence, it follows that the conjoined soul is turned toward phantasms in its possible intellect, as passive toward active, so that it can receive species only from them together with the agent intellect. But when separated from the body, just as it has another mode of existence without informing the body, so it has another mode of understanding; and, again from the conformity of its mode of operation to its mode of existence, it follows that the separated soul is turned in its intellect toward superior active things, so as to receive from them an influx of species, having been made like them in its mode of existence and, with the body left behind, having become in a certain way freer and no longer bound to phantasms.

From this there arises another difference: the conjoined soul cannot know immaterial substances except through species received from sensible things. Its intellect is bound to phantasms. But the separated soul can know them through their own species, since it is already turned toward superior things.

From these there also arises a third difference, noted by those who speculate subtly: the soul is part of the species and is united to the body for the sake of what is better. For the cognition that the soul has through acquired species is distinct and quidditative cognition, reaching to the ultimate differences of things. But the cognition that the separated soul receives from infused species is confused and makes things known in general. Since the soul is naturally part of man, it claims for itself, from its own nature, a natural mode of understanding: to understand through species received from phantasms, and not through infused species. For this mode of understanding is natural to intelligences by their nature; and therefore, just as intelligences have perfect knowledge of things through infused species, so the soul can have perfect knowledge of sensible things through acquired species. Infused species exceed the natural capacity of its intellect. This mode belongs connaturally and properly to a higher order, and belongs to the soul only through a deficient participation.

Moreover, since there is such an order among intellectual substances that the closer they are to the first substance, which penetrates all things by understanding through its own substance alone, the more naturally they grasp a perfect knowledge of things through more universal species, the last among them—the intellectual soul—by its nature requires species so articulated that it must have a likeness of each quiddity individually. For this reason it is united to the body, so that it may receive them from it. Consequently, when its intellectual power attempts to understand through superior species, such as infused species, it is in a way overwhelmed and has only confused knowledge, just as a student unable to grasp the teacher’s universal concepts remains without distinct cognition. A sign of this is that among human beings of keen intellect, once principles are proposed they immediately proceed to conclusions and derive many particular conclusions from the same principles. Those of dull intellect, however, perceive a distinct truth only when principles are applied by the teacher to each conclusion, in syllogistic form, and with material examples.

From this you can now understand that the soul, neither conjoined nor separated, can naturally have quidditative cognition of immaterial substances. What is more, from this you see that the separated soul, through infused species, knows neither an ox nor a lion quidditatively, but knows everything besides its own nature in general. Wherever else you find St. Thomas saying that the separated soul knows the quiddities of immaterial substances, remember that he calls quidditative cognition the cognition that the separated soul has of them through their proper species, which it cannot have.

To the first argument, then, it should be said that although understanding immaterial substances is the most noble operation of the intellectual soul, understanding them quidditatively is nevertheless an operation impossible for it. Nor did Aristotle say the opposite in Ethics I or X; indeed, the question raised by him in On the Soul III, text 36, is nowhere found solved. For he placed human happiness in the contemplation of separated substances, insofar as that is possible for us, whatever it may be.

To the second, similarly, it is said that the soul’s union with the body does not impede quidditative cognition of immaterial substances, since that cognition is impossible for the soul in every state of nature.

If these two arguments are framed to conclude that the united soul can have such knowledge of immaterial substances as the separated soul has through their species, the answer to the first is by denying that understanding immaterial substances in this way is, absolutely speaking, the soul’s most noble operation, although it is the most noble in a qualified respect. For understanding sensible substances distinctly and quidditatively, and immaterial substances through sensible effects and common notions, places absolutely a greater perfection in the soul than understanding them confusedly, although that confused understanding is in a qualified respect nobler because it is through their species and in a more immaterial manner. Hence I say that it is not unreasonable for our soul to be impeded from an operation most noble in a qualified respect, for the sake of acquiring through union with its proper matter the perfection that is absolutely most noble for it. It therefore does not follow that union is unnatural, but rather most natural, since it is for the sake of its absolute perfection—especially because the cognition it has when separated is, for it, quasi-unnatural, as is also the mode of existence it has.

To the second, let it be said that the soul is impeded by union with the body from receiving such an influx because its mode of operation follows its mode of existence in the body only through turning toward phantasms. For the soul’s natural turning toward phantasms impedes its turning toward superior things. The proof against this accomplishes nothing, since an impediment can be given in another way, as is now clear. To the confirmation, it is said that the minor is false. Understanding immaterial substances in this way is a good of the soul in a qualified respect, and not absolutely; whereas union with the body, together with what follows from it, is its good absolutely. To the third, it is said that whether existence and essence are distinguished or are the same, the point does not change. In God they are the same, while in the other intelligences they are distinguished; yet we state the same judgment about both, saying that we know existence, not quiddity. The response given there is therefore true, because it says that we know quiddity imperfectly. Nor does this conflict with the statements of the Thomists. Not with the first, because that must be understood of quidditative cognition, and not of cognition of every kind. Thus the inference “therefore we know nothing at all” is invalid; rather, “therefore we do not know quidditatively at all.”

Nor does it conflict in any way with the second statement. When, accustomed to Peripatetic language, we say that we know existence and not quiddity, we mean that we know how to settle for them the question whether it is, which asks about existence, and that we do not know how to settle for them the question what it is, which investigates quiddity—even if we know how to settle it according to some quidditative predicate. We call that knowledge that it is, and not quidditative knowledge, following Aristotle’s footsteps: in the Posterior Analytics he calls knowledge of a thing through common notions knowledge that it is. For this reason the Thomists proportionally deny of quiddity the knowledge that they affirm of existence: we are said not to possess knowledge concerning the proper question of quiddity, whereas we do not lack knowledge concerning the proper question of existence itself.

To the last argument, by which it is proved that the response is false in itself, I say that our intellect is said to know immaterial substances imperfectly because it cannot apprehend them quidditatively, and more imperfectly in this life because it knows them through species of other things. Although knowing them in the first way belongs only to the substances themselves, and it would be ridiculous to doubt whether what belongs to intelligences alone belongs to others, it is necessary to doubt whether knowing them quidditatively belongs to them alone or also to our soul. That knowing them in the second way is impossible for us in this life is said not voluntarily but by compelling reason. For the body united to the soul turns the soul toward itself and toward sensible things, as has been explained.

This, however, should be understood: genus and difference are not taken in the same way in those substances and in sensible substances. In sensible things, genus is taken from what is material in the thing, while difference is taken from what is formal in it. Hence Avicenna says at the beginning of his On the Soul that form, in things composed of matter and form, is the simple difference of that which is constituted from it—not that the form itself is the difference, but because it is the principle of the difference, as he says in his Metaphysics. Such a difference is called a simple difference because it is taken from what is a part of the thing’s quiddity, namely, form. But since spiritual substances are simple quiddities, their difference cannot be taken from what is a part of quiddity, but from the whole quiddity. Therefore Avicenna says at the beginning of On the Soul that only species whose essences are composed of matter and form have a simple difference. Likewise, in them genus is taken from the whole essence, but in a different way: one separated substance agrees with another in immateriality. They differ from one another in degree of perfection according to their recession from potentiality and approach to pure act. Therefore genus is taken in them from what follows them insofar as they are immaterial, such as intellectuality or something of this kind; but difference is taken from what follows in them according to their degree of perfection, which is nevertheless unknown to us.

Here is posited the second note, by which he explains, in comparison with sensible substances, from where difference is taken, and from where genus is taken, in immaterial substances.

For clarity on this point, know that in things composed of matter and form four things are understood: matter, which is one part of the specific composite; form, the remaining part; the whole quiddity insofar as it has the character of something capable of further formal perfection; and that same whole quiddity insofar as it has its ultimate formal perfection. For example, in man you can consider the matter in which his form is received, and the form received in it. You can also consider man himself insofar as he is a substance: man is a substance, and as a substance he has the character of something capable of perfection through corporeality, rationality, and so on. Consider also man insofar as he is of a rational nature, which is his ultimate formal perfection. These four stand in relation to genus and difference as follows. Matter, which is a part, the whole itself, and what is capable of perfection ground genus, though in different ways. Form, which is a part, and the whole itself insofar as it is perfected by a subsequent formal perfection, likewise ground difference in different ways. Since genus contains differences potentially, explains the nature of the thing incompletely and potentially, and signifies the whole according to what can still perfect it—and since the root of potentiality in sensible things is matter—it is rightly said to be taken from the whole insofar as it can be formally perfected, and from matter itself. Similarly, since to differ is to divide, delimit, and actualize, and to explain the whole according to a subsequent perfection and actuality—and since the root of actuality and perfection is form—difference is rightly taken from the whole insofar as it is perfected, and from form.

The parts of the thing—matter, form, and the whole quiddity as capable of and as possessing perfection—ground genus and difference in different ways. Genus is taken from the whole essence insofar as it has the character of what is capable of perfection, as from the thing formally signified or denominated by it; but from matter as from the root of its formal signification. Similarly, difference is taken from the whole essence according to a further perfection, as from the thing formally signified or denominated by it; but from form as from the root of its formal signification. Matter, which is a part of man, is not denominated his genus, nor form his difference; rather, man himself receives the denomination of genus insofar as he is a substance or animal, and has the denomination of difference insofar as he is corporeal or rational. Since matter and form radically ground genus and difference, Aristotle says in Metaphysics VII, text 33, that as the whole account stands to the whole thing, so a part of the account stands to a part of the thing. In Metaphysics VIII, text 9, you will find genus taken from matter and difference from form. Moreover, the Commentator says in On the Heavens II, commentary 49, that if heavenly bodies agree in genus and differ in species, they are composed of matter and form. You will also find distinguished men sometimes saying that genus is not taken from matter and difference not from form, because genus and difference are taken from the whole essence as from the thing signified by a name of first intention and denominated by a name of second intention, and not from a part. Once you have considered their reasons, you will see that they do not conflict with what was said above.

Since this is so, ascending from material substances to immaterial substances, we do not say that genus is taken from matter or difference from form, because they lack these parts. It therefore remains that in them both genus and difference are taken from the whole essence, not only formally but also radically. Hence Avicenna, as the text says, assigns a difference between the differences of composite and simple substances, saying that the difference in species composed of matter and form is simple, but the difference of non-composite things is not. He calls that a simple difference which does not proceed radically from the whole, but comes from a part of it that is simple. Thus in immaterial substances genus and difference are taken from the whole essence, but differently: genus is taken from the whole essence according to that in which one essentially resembles another, for intelligences agree in some quidditative predicate. Difference, however, is taken from the whole essence according to that in which one differs substantially from the others. This is a certain formally indivisible degree of formal perfection; the closer an intelligence has been allotted to the most pure act, the glorious God, the more perfect it will be. For they differ from one another in that one is closer than another to pure act and recedes farther from the nature of potentiality.

For a fuller understanding of these matters, we must begin more deeply. It should be known that speaking of genus and difference simply and according to what happens to them and belongs to them per se is one thing; speaking of them insofar as they are applied to such natures is another. If we speak of them in themselves, then for the account of both genus and difference it is required and sufficient that difference explain a certain limited degree of being, belonging to no extraneous nature relative to the nature of the genus, of which it is formally divisive, while genus explain a certain nature formally determinable. The first of these points follows from the fact that difference, coming to genus, constitutes the species and places it in the determinate degree of being that it explains. Hence in Metaphysics VIII, commentary 10, species are likened to numbers: just as numbers are changed by subtracting or adding a unit, so difference itself diversifies beings when added or subtracted. The second follows from the fact that difference must diversify genus, so that not only is one species different from another, but the nature of the genus in one species is different from the nature of the genus in another, as is found in Metaphysics X, text 24. Hence Aristotle says in On Animals XI that if figure were to be divided, its differences would not be “having angles equal to two right angles” and “having angles equal to many right angles,” because these are accidents of figure. Genus must signify a certain nature, so that transcendentals are excluded, and it must be formally determinable, so that the most specific species are set apart.

If we speak of genus and difference as applied to material substances, genus not only explains the thing as formally determinable, but is also radically taken from matter; and difference likewise not only signifies the determination and actualization of genus, but is radically taken from form. These features accrue to genus and difference because the essence whose predicates they are is composed and really integrated from two principles, namely determinable matter and determining form. It belongs per se to animal to signify a sensitive nature formally determinable by rationality. But because sensitive nature is determinable by rationality because it has matter, it happens to this genus, animal, insofar as it is a genus, that it is taken from matter. If sensitive nature were determinable by rationality and not by reason of matter, animal would be no less a genus. Similarly, rationality per se signifies a reasoning perfection essentially determinative of sensitive nature. But because the intellectual grade determines the sensitive grade because the intellectual soul is the form of the body, it happens to this difference, rationality, insofar as it is a difference, that it is taken from form. Rationality would be no less a difference if reasoning perfection determined the sensitive without informing a body. For this reason it is commonly said that genus is taken from what is material rather than from matter, and difference from what is formal rather than from form. The former belongs to them per se; the latter accidentally.

Since the simple essence of immaterial substances is determined and defined to a certain degree of perfection, since it is not of infinite being, it follows that in it there is something from which genus and difference can be taken. From the fact that the nature is limited, difference is taken from its very determination. From the common nature, which is understood as determinable, genus is taken. But from the fact that it is simple, it is terminated by itself, so that it does not have two real parts, one of which is terminated and the other terminates, as sensible substances have matter and form.

Thus, in taking genus and difference in immaterial substances, what belongs per se is preserved: genus signifies a certain nature formally determinable, and difference explains a determinate substantial perfection formally constituting it in a certain degree of being. What belongs accidentally is not preserved, namely, that genus is taken from matter and difference from form.

For a deeper investigation of this matter, three propositions must be noted. The first is that every individual really distinct from its own existence has several quidditative predicates, by the succession of which it approaches more and more closely to its existence. The second proposition is this: among the aforesaid quidditative predicates there is such an order that each is more actual the more closely it approaches existence, and more potential the farther it is from existence. These propositions are explained first by examples, then by reasoning.

Socrates, really distinct from his existence, has several quidditative predicates, namely substance, body, living thing, animal, and man. It is certain that Socrates insofar as he is a substance is very far removed from his existence: for Socrates to be, it is required not only that he be a substance, but also that he be a body. When you take Socrates insofar as he is a body, he appears closer to having existence, although he is still quite far from it: for Socrates to be, it is required not only that he be a corporeal substance, but also that he be living. When you consider Socrates as living, you will see him approach being more closely, though he is still remote: for Socrates to be, it is required not only that he be an animate substance, but also that he be an animal. When you inspect him insofar as he is an animal, you will find him closer to existing, though still remote, because for Socrates to be it is required not only that he be an animate, sensible substance, but also rational; for nothing can be contained in nature under some genus unless it is contained under some species. When he is considered as an animate, sensible, rational substance, he can then receive actual existence: nothing else intrinsic and formal is required for him to be, although extrinsic causes and an individual property are required as the condition of an existent. The predicates introduced plainly stand in such a relation that what is closer to existence, compared with what is more remote, stands as actual to potential: man to animal, animal to living thing, living thing to body, and body to substance. Consequently, what is closer to existence itself is more actual, while what is farther from existence is more potential; and thus both propositions are exemplified.

I prove it by reasoning. Since existence is the most actual of all things in a thing, and is of such actuality that it is the proper act only of a completed essence, for an essence to become its recipient it must be intrinsically complete and determined. Just as, for air to receive light, it must first be perfected by transparency, so substance is terminated, perfected, and completed by these quidditative predicates. Therefore, the more a quidditative predicate determines the essence, the more it appropriates the essence to be the proper recipient of existence itself. Conversely, the less a quidditative predicate determines the essence, the less it appropriates it so that it may be capable of existence itself. Since each thing is more actual the closer it is to what is most actual, and more potential the farther it is from it, there is therefore among quidditative predicates such an order that what is closer to existence itself is more actual, while what is remote is more potential.

Once these two propositions have been given, if you add a third—namely, that genus is taken from what is potential, while difference is taken from what is actual—the most general rule follows: genus and difference in all things are taken from the whole essence of the thing according to its remoteness from and proximity to existence itself. For the ultimate difference, since it constitutes the species and gives it its proper degree among beings, is the ultimate completion of the essence, so that it may be. Beyond it, as has been said, the individual expects no other intrinsic completion in order to be. The most general genus, since it explains the essence as most determinable, is taken from that by which the essence is most remote from existence: namely, as determinable and perfectible by all the differences so that it may receive existence. Intermediate genera and differences are taken from intermediate factors (and for this reason it is said that definition explains the defined thing from first potency to ultimate act). For it includes the first genus, taken from that by which the essence can first have existence, and all the differences by which the essence is gradually determined and actualized up to the ultimate difference, which is the act finally determining and perfecting it so that it may have existence. Hence Porphyry also says that, for those who investigate more deeply, difference is what concludes toward existence.

Yet by what we have said we do not mean that genus and difference are taken from actual existence; for we know that definitions abstract from existence. We mean that genus and difference are taken, in St. Thomas’s words, from their order to actual existence. When we say “from order,” we do not mean the relation of order, but its foundation: from that by which the essence approaches existence as something receptive, and from that by which the essence is remote from existence. From these principles you can see where genus and difference are taken in intelligences, material substances, and accidents, as anyone practiced in these matters can readily work out in each case. For this reason God alone lacks genus and difference. His quiddity, being his actual existence, cannot be conceived as remote from existence or close to it. Thus St. Thomas assigned a most sufficient reason at the beginning of this chapter why God is not in a genus while intelligences are in a category: he is his own existence, whereas their essence is distinct from their proper existence.

Nor need these differences be accidental, since they are according to greater and lesser perfection, which does not diversify a species. A degree of perfection in receiving the same form does not diversify a species, as something whiter and less white in participating in whiteness of the same species; but degrees of perfection in the forms or natures themselves that are participated do diversify a species. Thus nature proceeds by degrees from plants to animals, through certain things that are intermediate between animals and plants, according to the Philosopher in On Animals.

Here the first objection is excluded. It was said that differences in intelligences are taken from diverse degrees of perfection, by which one is closer than another to the first act. The objection runs as follows: whatever differ according to a perfecter and a less perfect act differ only by accidental differences; intelligences differ only according to what is more and less perfect; therefore they differ only by accidental differences. The reasoning is valid, but the conclusion is false; therefore one of the premises is false. It is not the major, as will be proved, and so it is the minor, which is the position stated above. The major is proved because more and less do not vary a species: perfect and less perfect whiteness belong to one species; but whatever belong to the same species are distinguished only by accidental differences, since they agree in all essential respects. This objection is excluded by the beautiful distinction that perfecter and less perfect may be considered either with respect to the mode of possessing one form simply, or with respect to the forms themselves, possessed in greater or lesser perfection. In the first way they do not vary a species, but in the second they do. For whatever receive a single form according to diverse degrees of perfection are distinguished only numerically as such, as is clear of white things, in On White IV and VI. But those that receive diverse degrees of perfection not of one form but of several forms must be distinguished essentially or specifically, as is clear of man and ox. The answer to the objections is therefore clear: in the first way the minor is false, in the second way the major is false. The reason why the proof of the major seems to be commonly given without qualification is that the comparison signified by “more” and “less” properly occurs only within an atomic species, as is said in Physics VII, commentary 27.

Nor again is it necessary that the division of intellectual substances always be by real differences, since it is impossible for this to occur in all things, as the Philosopher says in On Animals XI.

Here the second objection is excluded. The objection against the same statement is made as follows: wherever there are a true genus and true species, there must be an artificial division of that genus by two true differences; but in intelligences there are a true genus and true species; therefore there must be a division there by two true differences. The conclusion conflicts with the division assigned above, in which it was said that the genus of intelligences descends to its species through more and less perfect, which are not true differences. The major is proved because wherever a true genus with true species is found, there must be differences that divide the genus and constitute the species; and because a division according to art must be two-membered, as Boethius testifies. St. Thomas excludes this objection by saying that the major is universally impossible according to Aristotle’s view in Book II of On Animals. For clarity, note that since true differences are called positive differences, not extraneous, contrary to one another, and convertible with the things whose differences they are, as Aristotle says there in chapter III, a genus that immediately contains more than two species cannot be divided immediately by two true differences. If it is to be divided by true differences that exhaust its power, it must be divided by more than two, and the division will not be two-membered. If it must be divided into two members, one difference must not be true, for it will be taken with the privation of the other. Thus, if animal immediately contains man, ox, and lion, it must be divided by three true differences, or by one true difference, say rational, and another not true but privative and common to the other two, say irrational.

Since, then, some things in the world immediately contained under some formally divisible common thing are more than two in number, it is said to be universally impossible that every division be by two true differences. This occurs in our case. Since intelligences lack a subaltern genus, as St. Thomas testifies in his treatise On the Nature of Genus, chapter V, because their perfection does not arise from several combinations of differences as the perfection of species among lower things does, and since a common genus and difference are insufficient for those lower things, all intelligences will be immediately contained under one genus. If their genus must descend to them by true differences, the division would have to be many-membered and unknown to us. If it is contracted by a twofold division, one member must simply not be true, because it is privative; and, because of the weakness of our intellect, unable to descend to any proper difference of theirs, the other must also not be true. Such were the differences assigned in the text: the more perfect and the less perfect.

The answer to the objection is now clear, since the universal impossibility of the major has been explained. Boethius’s statement does not conflict with this. Although he says that every division is reduced to a two-membered division, he does not say that every two-membered division is made through true differences of the lower things to be taken by that division.

In a third way this is found in substances composed of matter and form. In them existence is received and finite, and therefore they have existence from another; moreover, their nature or quiddity is received in designated matter. Hence they are finite both above and below, and in them, through the division of designated matter, the multiplication of individuals in one species is possible. What was said above explains how essence and logical intentions stand in these substances.

In this fourth and final part of the chapter he gathers four points about the essences of composite substances. First, their existence is limited, because they have it from another, being really distinct from themselves; and by this they are first distinguished from the first being, whose existence is infinite and really identical with its quiddity.

Second, their essence is received in designated matter: they are determined to this or that, to a here and now, as the formal is determined through its material.

Third, what follows as a corollary from these two is that they are finite above and below. Above, because they have limited existence, and their essence is terminated by that existence, which it regards as above. Below, because their forms are received in matter and are terminated to this and that, which they regard as below, by being received in these and those material conditions as in a material part.

Fourth, their essence can be multiplied numerically within the same species because of the division of designated matter. By these three points they differ from intelligences, placed in the second order, which are free from matter and, being infinite below, admit no equal to themselves. Thus the second treatise of this book comes to an end.