Commentary Aristotle Posterior Analytics
Lecture 18
Coexistence of cause and caused
a35. The question might be raised with regard to cause and effect whether when the effect is present the cause also is present; whether, for instance, if a plant sheds its leaves or the moon is eclipsed, there is present also the cause of the eclipse or of the fall of the leaves — the possession of broad leaves, let us say, in the latter case, in the former the earth’s interposition.
b2. For, one might argue, if this cause is not present, these phenomena will have some other cause: if it is present, its effect will be at once implied by it — the eclipse by the earth’s interposition, the fall of the leaves by the possession of broad leaves; but if so, they will be logically coincident and each capable of proof through the other.
Let me illustrate: Let A be deciduous character, B the possession of broad leaves, C vine. Now, if A inheres in B (for every broad-leaved plant is deciduous), and B in C (every vine possessing broad leaves); then A inheres in C (every vine is deciduous), and the middle term B is the cause. But we can also demonstrate that the vine has broad leaves because it is deciduous. Thus, let D be broad-leaved, E deciduous, F vine. Then E inheres in F (since every vine is deciduous), and D in E (for every deciduous plant has broad leaves): therefore every vine has broad leaves, and the cause is its deciduous character.
b16. If, however, they cannot each be the cause of the other (for cause is prior to effect, and the earth’s interposition is the cause of the moon’s eclipse and not the eclipse of the interposition) — if, then, demonstration through the cause is of the reasoned fact and demonstration not through the cause is of the bare fact, one who knows it through the eclipse knows the fact of the earth’s interposition but not the reasoned fact.
b22. Moreover, that the eclipse is not the cause of the interposition, but the interposition of the eclipse, is obvious because the interposition is an element in the definition of eclipse, which shows that the eclipse is known through the interposition and not vice versa.
b25. On the other hand, can a single effect have more than one cause? One might argue as follows: if the same attribute is predicable of more than one thing as its primary subject, let B be a primary subject in which A inheres, and C another primary subject of A, and D and E primary subjects of B and C respectively. A will then inhere in D and E, and B will be the cause of A’s inherence in D, C of A’s inherence in E. The presence of the cause thus necessitates that of the effect, but the presence of the effect necessitates the presence not of all that may cause it but only of a cause which yet need not be the whole cause.
b32. We may, however, suggest that if the connexion to be proved is always universal and commensurate, not only will the cause be a whole but also the effect will be universal and commensurate. For instance, deciduous character will belong exclusively to a subject which is a whole, and, if this whole has species, universally and commensurately to those species—that is, either to all species of plant or to a single species. So in these universal and commensurate connexions the ‘middle’ and its effect must reciprocate, that is, be convertible. Supposing, for example, that the reason why trees are deciduous is the coagulation of sap, then if a tree is deciduous, coagulation must be present, and if coagulation is present—not in any subject but in a tree—then that tree must be deciduous.
The question might be raised. After showing how one should investigate 'propter quid', the Philosopher now raises two questions in regard to 'propter quid'.
The first of these concerns the co-existence of cause to caused.
The second pertains to the unity of cause, at: can the cause of an identical effect (100a1; [575]).
Concerning the first he does three things.
First, he proposes the question.
Second, he raises an objection, at: for, one might argue (99b2; [568]).
Third, he solves the question, at: on the other hand, can a single (99b25; [573]).
He says therefore first (99a35) that in regard to cause and caused, it is possible to wonder whether, when one of them exists, does the other also exist? (However, this question should not be interpreted as referring to coexistence in time but of succession, such that if one is posited, does the other follow regardless of whether they are concurrent in time, or before and after.)
And he gives two examples.
In one of them, the cause precedes the caused in time: for the cause why the leaves of a tree fall off is that it has broad leaves; for the possession of broad leaves and their falling are not simultaneous in time.
In the other example, the cause and the caused are simultaneous in time; as the interposition of the earth is simultaneous in time with the eclipse of the moon. The question, therefore, is whether upon the one of them the other follows.
Then, at: for, one might argue, if this (99b2) he objects to the question proposed and shows that cause and caused are always together as to succession.
He gives two reasons for this.
The first one is based on the notion of cause and caused. And he says that every caused thing must have some cause. Hence, if something is posited as caused and it is not simultaneously posited that such and such is its cause, it follows that something else is its cause, and hence it is necessary that something caused is simultaneous with a certain cause. For example, from the fact that the earth is in the middle, it follows that the moon is eclipsed; and from the fact that a tree has broad leaves, it follows that its leaves fall off. Therefore, if there is no other cause, it follows that this caused is simultaneous with its cause.
Then, at: let me illustrate (99b2) he gives the second reason which is based on the fact that cause and caused are demonstrated the one by the other.
Concerning this he does three things.
First, he states the reason.
Second, he dismisses the error that could follow, at: if, however, they cannot each (99b16; [571]).
Third, he proves what he had presupposed, at: moreover, that the eclipse (99b22; [572]).
In regard to the first he says (99b2) that it is also manifest that cause and caused follow upon one another simultaneously, if it is true that either can be demonstrated by the other: because the conclusion of a demonstration follows of necessity from the middle. But the fact that either can be demonstrated by the other is shown by the following example: Let leaf falls off be A, the major extreme; to have a broad leaf be B, the middle; and vines be C, which is the minor. Thus, therefore, A is in B, (because whatever has broad leaves loses its leaves); but B is in C, (because every vine has broad leaves). And so it is concluded that A is in C, because every vine loses its leaves. Now, in this whole process the cause is taken as middle; consequently, the caused is demonstrated by the cause. But it is also possible conversely to demonstrate the cause through the caused, namely, that a vine has broad leaves because its leaves fall off. For we may take as D, the major term, the fact of having broad leaves; and as E, the middle, the fact that the leaves fall off; and as Z, vine, which is the minor extreme. Thus, therefore, E is in Z, (because from every vine the leaves fall off); but D is in E, (namely, everything whose leaves fall off has broad leaves.) From this it is concluded that every vine has broad leaves, which is taken as the cause accounting for the leaves falling off.
Then, at: if, however, they cannot each (99b16) he excludes an error which could follow from the foregoing, namely, that according to the same reason one of the foregoing may be demonstrated from the other.
But he rejects this, saying that if it does not occur that the two given things are mutually causes one of the other, namely, in the same genus of cause (since the cause is prior to that of which it is the cause, and it does not occur that a same thing is prior and subsequent in the same way), then since the cause of the eclipse of the moon is the fact that the earth is between, it is not possible that the eclipse of the moon is the cause of the earth’s being between. Therefore, if a demonstration through cause is a demonstration 'propter quid', whereas one which is not through the cause is demonstration of the 'quia', as was established in Book I, it follows that one who demonstrates through the eclipse of the moon that the earth is between, knows 'quia' not 'propter quid'.
Then, at: moreover, that the eclipse (99b22) he proves what he had supposed, namely, that the interposition of the earth is the cause of the eclipse and not the converse.
And he says that it is obvious that the eclipsing of the moon is not the cause of the earth’s being between, but it is rather the converse; because in explaining an eclipse it is stated that the earth is between, as has been stated. Therefore, since 'quid' and 'propter quid' are the same, it is clear that the eclipse of the moon is known through the fact that the earth is between, as through a middle which is 'propter quid'; and not conversely.
Then, at: on the other hand, can a single (99b25) he solves the proposed question, showing the cases in which it is true that cause and caused always follow upon one another, and the cases in which it is not true.
Concerning this he does two things.
First, he shows the cases in which it is not true.
Second, those in which it is true, at: we may, however, suggest (99b32; [574]).
He says therefore first (99b25) that one common thing happens to have several causes, insofar as it is found in diverse things; as to be worthy of blame belongs to a rash person because of excess, but to a timid person because of a deficiency. Therefore, let us assume that some thing is predicated of several things chiefly and immediately, that is, that A is predicated in a first way of B and also of C; as to be blameworthy is predicated of excessiveness and deficiency. Let us further assume that these two, namely, C and B, are predicated of D and E; as excessiveness of rash, and deficiency of timid. Therefore, A will be predicated of D and of E, because both the rash and the timid are blameworthy. But the cause of A’s being in D is B; (for a rash person is blameworthy because of excess.) But the cause of A’s being in E is C; (for a timid person is blameworthy because of defect). It is clear, therefore, that since the cause exists, the thing must exist: (because whether A is excess or defect, it is necessary that something be blameworthy). On the other hand, if the thing exists, it is necessary that one of the causes exist, although it is not necessary that both causes exist. (For example, supposing that something is blameworthy, it is not necessary that it be due to excess, but it is necessary that it be due either to excess or to defect).
Then, at: we may, however, suggest (99b32) he shows in which cases it is necessary that cause and caused follow one another simultaneously.
And he says that if something be asked in a universal way, and if both the cause and that whose cause is sought be taken in a universal way, then it is required that the effect always follow upon the cause, and the cause upon the effect. Thus the fact of losing leaves does not belong in a first way to several things as it did in the above example, but it belongs determinately to one common first thing; although of that common thing there are many species, to which it belongs universally that their leaves fall off: say, if we took either plants or this type of plant, namely, the type that has broad leaves. Hence in all of these it is required to take an equal middle, so that the cause and that of which it is the cause are converted. Thus we might inquire why trees lose their leaves: if the cause of this is taken to be the fact that the moist element has hardened and made easier to dry out, it will follow that if the effect exists, the cause also exists; for example, if the tree has its leaves falling off, it is required that there be a hardening of its moist element. Conversely, it is required that if the cause is posited, then the effect is posited in such a thing: thus if the hardening of the sap exists, it follows not of anything at random but of the tree, that the leaves fall off.