Commentary Aristotle Posterior Analytics
Lecture 7
The two ways, logical and demonstrative, of manifesting quod quid a1. We must now start afresh and consider which of these conclusions are sound and which are not, and what is the nature of definition, and whether essential nature is in any sense demonstrable and definable or in none.
a4. Now, to know its essential nature is, as we said, the same as to know the cause of a thing’s existence, and the proof of this depends on the fact that a thing must have a cause. Moreover, this cause is either identical with the essential nature of the thing or distinct from it; and if its cause is distinct from it, the essential nature of the thing is either demonstrable or indemonstrable. Consequently, if the cause is distinct from the thing’s essential nature and demonstration is possible, the cause must be the middle term, and, the conclusion proved being universal and affirmative, the proof is in the first figure. So the method just examined of proving it through another essential nature would be one way of proving essential nature, because a conclusion containing essential nature must be inferred through a middle which is an essential nature just as a ‘peculiar’ property must be inferred through a middle which is a ‘peculiar’ property; so that of the two definable natures of a single thing this method will prove one and not the other. Now, it was said before that this method could not amount to demonstration of essential nature—it is actually a dialectical proof of it — a16. so let us begin again and explain by what method it can be demonstrated. When we are aware of a fact we seek its reason, and though sometimes the fact and the reason dawn on us simultaneously, yet we cannot apprehend the reason a moment sooner than the fact; and clearly in just the same way we cannot apprehend a thing’s definable form without apprehending that it exists, since while we are ignorant whether it exists we cannot know its essential nature.
a21. Moreover we are aware whether a thing exists or not sometimes through apprehending an element in its character, and sometimes accidentally, as, for example, when we are aware of thunder as a noise in the clouds, of eclipse as a privation of light, or of man as some species of animal, or of the soul as a self-moving thing.
a24. As often as we have accidental knowledge that the thing exists, we must be in a wholly negative state as regards awareness of its essential nature; for we have not got genuine knowledge even of its existence, and to search for a thing’s essential nature when we are unaware that it exists is to search for nothing. On the other hand, whenever we apprehend an element in the thing’s character there is less difficulty. Thus it follows that the degree of our knowledge of a thing’s essential nature is determined by the sense in which we are aware that it exists.
a28. Let us then take the following as our first instance of being aware of an element in the essential nature. Let A be eclipse, C the moon, B the earth’s acting as a screen. Now, to ask whether the moon is eclipsed or not is to ask whether or not B has occurred. But that is precisely the same as asking whether A has a defining condition; and if this condition actually exists, we assert that A also actually exists. Or again we may ask which side of a contradiction the defining condition necessitates: does it make the angles of a triangle equal or not equal to two right angles? When we have found the answer, if the premises are immediate, we know fact and reason together; if they are not immediate, we know the fact without the reason, as in the following example: let C be the moon, A eclipse, B the fact that the moon fails to produce shadows though she is full and though no visible body intervenes between us and her. Then if B, failure to produce shadows in spite of the absence of an intervening body, is attributable to C, and A, eclipse, is attributable to B, it is clear that the moon is eclipsed, but the reason why is not yet clear, and we know that eclipse exists, but we do not know what its essential nature is. But when it is clear that A is attributable to C and we proceed to ask the reason of this fact, we are inquiring what is the nature of B: is it the earth’s acting as a screen, or the moon’s rotation or her extinction? But B is the definition of the other term, viz. in these examples, of the major term A; for eclipse is constituted by the earth acting as a screen. Thus, (1) ‘What is thunder?’ ‘The quenching of fire in cloud’, and (2) ‘Why does it thunder?’ ‘Because fire is quenched in the cloud’, are equivalent. Let C be cloud, A thunder, B the quenching of fire. Then B is attributable to C, cloud, since fire is quenched in it; and A, noise, is attributable to B; and B is assuredly the definition of the major term A. If there be a further mediating cause of B, it will be one of the remaining partial definitions of A.
b15. We have stated then how essential nature is discovered and becomes known, and we see that, while there is no syllogism—that is, no demonstrative syllogism—of essential nature, yet it is through syllogism, viz. demonstrative syllogism, that essential nature is exhibited. So we conclude that neither can the essential nature of anything which has a cause distinct from itself be known without demonstration, nor can it be demonstrated; and this is what we contended in our preliminary discussions.
We must now start afresh. After inquiring disputatively how the definition and the 'quod quid' are known, the Philosopher here determines the truth.
First, he states what his intention is.
Second, he carries out what he proposes, at: now, to know its essential (94a4).
Third, he summarizes, at: our discussion has therefore made plain (95a13).
He says therefore first (94a1) that after the disputative process we must once more consider, but this time by establishing the truth, how much of the foregoing has been well stated and how much not well stated: and this both in regard to definition, by considering what a definition is, and in regard to 'quod quid', by considering whether it might somehow or other be manifested through a definition or a demonstration or not at all.
Then, at: now, to know its essential (94a4) he carries out what he has proposed.
First, in regard to the 'quod quid'.
Second, in regard to definition which is a statement signifying it, at: since definition is said to be (94b28).
Concerning the first he sets down two methods of manifesting the 'quod quid'.
First, the method of logical proof.
Second, the method of demonstrative proof, at: so let us begin again (94a16).
Regarding the first he reviews first of all (94a4) that which was established above, namely, that it is the same thing to know quid est and to know the cause involved in the question 'an est', just as it is the same thing to know 'propter quid' and to know the cause involved in the question 'quia' est. The reason for this, that is, for the fact that it is the same thing to know the 'quid est' and the cause involved in the 'si est', is that there must be some cause of the fact that a thing exists, (for something is referred to as caused by reason of the fact that it has a cause of its existing.) Now, the cause of existing is either the same, that is, the same as the essence of a thing, or not the same: (the same, indeed, as matter and form, which are parts of the essence; not the same, as agent and end, which two causes are somehow the cause of the form and matter, for the agent acts for an end and unites the form to the matter). And if we consider the cause which is other than the essence of a thing, sometimes it is such a cause that a demonstration can be formed in virtue of it, and sometimes not. For the effect does not follow of necessity from every efficient cause; but from the supposition of the end it follows that what is required for the end also exists, as is proved in Physics II.
So let us suppose that an effect exists which has as its cause not only the essence of the thing but also another cause such that something can be demonstrated through it; for example, we might say that if a man has attained happiness, it is necessary that virtue preexist. Now, let us assume that the essence of virtue is 'a habit which operates according to right reason'. Therefore, it can be demonstrated that there is a habit which operates according to right reason, if there is a habit conducive to happiness. Let that other cause, therefore, which is demonstrative, be taken as the middle, and let a syllogism be formed in the first figure (which must be done, because the 'quod quid' must be universally and affirmatively predicated of the thing of which it is the quod quid): the syllogism then will be: "every habit conducive to happiness is a habit operating according to right reason; but virtue is such a habit: therefore, etc."
He concludes, therefore, that this method which is now being examined is one method of showing the 'quod quid' through something else which is a cause. And this method is evidently suitable, because, as was established above, it is necessary that the middle taken for proving 'quod quid' be the 'quid est'; and similarly that the middle taken for proving properties be something proper. But there is the further consideration that since the 'quid est' is the cause of the very being of the thing, then according to the diverse causes of one thing, there are various ways of assigning the 'quod quid' of the same thing. For example, the 'quod quid' of house can be formulated in terms of its material cause, so that we might say that it is something composed of wood and stones; and also in terms of the final cause, namely, that it is an artifact constructed for habitation. Thus, therefore, it will occur that since there are several 'quod quid’s' of the same thing, one of them will be demonstrated and another not demonstrated but supposed. Hence it does not follow that there is a begging of the question, because one 'quod quid' is supposed and the other proved. Nor is this a method proving the 'quod quid' demonstratively, but of syllogizing it logically, because by this method it is not sufficiently proved that what is concluded is the 'quod quid' of the thing of which it is concluded, but merely that it is in it.
Then, at: so let us begin again (94a16) he shows how by demonstration the 'quod quid' can be achieved.
Regarding this he does two things.
First, he shows how the 'quod quid' can be manifested in certain instances through demonstration.
Second, he shows that it is not so in all cases, at: now, while some things (94b22).
Concerning the first he does three things.
First, he lays down certain things needed for showing what he proposes.
Second, he manifests what he has proposed, at: let us then take the following (94a28).
Third, he summarizes, at: we have stated then how essential (94b15).
With respect to the first (94a16) he lays down three things.
The first of these is a comparison between the 'quod quid' and the 'propter quid'.
He says, therefore, that in order to show how it occurs that the 'quod quid' can be achieved through demonstration, we must start once more from the beginning. The first thing to be considered is the fact that a person may be in either of two states as regards knowledge of the 'propter quid'. For sometimes we have the 'quia' in our knowledge and are still seeking the 'propter quid'; and sometimes both are manifest to us at one time. A third case is impossible, namely, that one know the 'propter quid' of something before the 'quia'. And the same holds for the 'quod quid erat esse': sometimes we know a thing to be without perfectly knowing the quid sit; sometimes we know both at once. Again, a third case is impossible, namely, to know quid est without knowing if it is.
Then, at: moreover, we are aware (94a21) he lays down the second preliminary remark.
He says that there are two ways in which we might know something to be without perfectly knowing the quid est: in one way, insofar as we might know one of its accidents, as for example, when by the speed of its motion we judge that something is a hare; in another way, by knowing something of its essence. (This of course is possible in the case of a composite substance, as when we comprehend something to be a man in virtue of the fact that it is rational, without yet knowing the other items which complete the essence of man. However, in simple substances this does not occur, because one cannot know anything concerning the substance of a simple thing without knowing the entire essence, as is clear from Metaphysics IX.) At any rate, a person who knows something to be must know it through something of that thing, namely, something outside the essence of the thing or something pertaining to its essence. And he clarifies this with the example of knowing thunder to be, because we perceive a sound in the clouds—which of course pertains to the essence of thunder, albeit not the entire essence, because not every sound in the clouds is thunder—or of knowing a defect, that is, an eclipse, of the sun or moon to be, because there is a failure of light—although not every failure of light is an eclipse. And the same applies if someone perceives a man to be, because there is an animal; or a soul to be, because something is moving itself.
Then, at: as often as we have accidental (94a24) he sets forth the third preliminary remark.
He says that those things which we know to exist through some accident belonging to them are such that there is no correlation between this knowledge and knowledge of their 'quid est', because in virtue of such accidents we do not even truly know that they are. We do of course know these accidents to be theirs, but because the accidents are not the things themselves, we do not thereby know that the things themselves exist. Moreover, it is fruitless to seek the quid est if one does not know quia est; but those things which we know to exist through something of their own can be more easily known by us as to what they are. Hence it is plain that as we are in regard to knowing 'that something is', so we are in regard to knowing 'what it is'.
Then, at: let us then take the following (94a28) in the light of the foregoing he manifests what he proposed.
And he says that in regard to a thing which we know exists because we know something of its essence, let us consider the following example in which A, the major extreme, is defect, that is, eclipse; and in which C, the minor extreme, is moon; and interposition of the earth between sun and moon is B, the middle. In this case, therefore, to ask whether the moon is eclipsed or not is the same as to ask whether B exists or not; but to ask whether B exists or not is to ask if there is some reason for that eclipse. For B, that is, the interposition of the earth, is the reason for the moon’s eclipse; and if there is an interposition of the earth we say that the other exists, that is, the eclipse of the moon. Or, similarly, if we should seek the reason for one side of a contradiction, that is, does it lie in having or in not having two right angles. But when we find that what we seek exists, for example, that there is an eclipse, then we know the 'quia' and the 'propter quid' at once, if what is sought is found through an appropriate middle which is the cause; and if not, but it is found through something extrinsic, we will know the 'quia' and not the 'propter quid'. For example, let the moon be C and the eclipse A, and let us take as middle, that is, B, the fact that the moon, although it is full, is now unable to cause a shadow when we put an object between it and us. For the moon, whenever it is not eclipsed, causes a shadow if some body is interposed; yet the fact that it is now unable to cause a shadow is not the cause of the eclipse, but rather its effect. Therefore, if B be predicated of C (that is, that the moon is now unable to produce a shadow of an object which is interposed), and if moreover A is true of that middle (that is, if we assume that whenever this happens, the moon is eclipsed), it will be plain that the moon is eclipsed. But it will not yet be clear 'why' the moon is eclipsed. Similarly, we will know 'that' there is an eclipse but not know what an eclipse is, when it is clear that A is in C, that is, that the moon is eclipsed. Now, just as in this example neither the 'propter quid' nor the 'quid' is known, so to inquire 'why' [that is, propter quid] something is, is the same as to inquire [quid], that is, what it is.
Thus, if we should ask propter quid, that is, why the moon is eclipsed, namely, is it because the earth is between the sun and moon, or because the moon has turned, that is, because the dark side of the moon has been turned toward us, as some say, or even because the light of the moon has been extinguished in something moist: to ask whether it is due to any of these causes that the moon is eclipsed is nothing more than to ask whether the eclipse of the moon consists in the interposition of the earth, or the turning of the moon, or the extinction of its light.
And this middle is the reason of the other extreme: thus, in the foregoing example, it is the reason for A which is the major extreme, because the eclipse of the moon is nothing more than the moon’s light being blocked by the earth. He gives a further example, namely, inquiring what is thunder. According to the opinion of Anaxagoras and Empedocles it is the quenching of fire in a cloud; (although according to his own opinion in Meteorology II, thunder is caused by a dry exhalation in a cold environment beating against a cloud. But he frequently uses the opinions of others in his examples.) So, if according to the above-mentioned opinion, one should ask why it thunders, the answer might be given that it is because fire is being quenched in a cloud. Therefore, let the cloud be C, the minor extreme, and thunder A, the major extreme, and the quenching of fire B, the middle. Then we may syllogize in the following manner: "In C is B, that is, in the cloud is a quenching of fire; but every quenching of fire is a sound: therefore in the cloud is a sound of thunder." And thus it is clear that to arrive at the 'propter quid' through demonstration, we take the 'quid est', because the very middle which shows the 'propter quid' is a statement defining the first term, that is, defining the major extreme. But if we had to take some other middle to demonstrate this, it would be taken from the remaining statements, that is, from the definition of the minor extreme and of other extrinsic causes. For since the subject is the cause of its proper attribute, it is required that the definition of the proper attribute be demonstrated by the definition of the subject. And this is clear in the other example;
for since the moon is a body fixed by nature to move in such and such a way, it is necessary that at some time the earth be interposed between it and the sun.
Then, at: we have stated then (94b15) he sums up what has been said.
He says that it has been said how the 'quod quid' is taken and made known, namely, by taking the 'propter quid'. We have also said that there is neither syllogism nor demonstration of the 'quid est' in the sense of properly syllogizing or demonstrating the 'quod quid', although the 'quod quid' is manifested by syllogism and demonstration, insofar as the middle in a 'propter quid' demonstration is the 'quod quid'. Hence, it is clear that a 'quod quid' having another cause cannot be known without a demonstration, but the demonstration is nevertheless not of the 'quod quid', as was proved in the objections. And according to this the above objections are true.