Commentary Aristotle Posterior Analytics
Then, at: we may add that if dialectical (98b38) he excludes a certain method of procedure in definitions.
He says that just as one cannot dispute by metaphors, so he may not define by metaphors; for example, by stating that man is an inverted tree. Furthermore, in definitions one may not use anything stated metaphorically. For since definitions are the most important and most efficacious middles in disputations, it would follow, if definitions were stated in metaphorical terms, that one would have to dispute by metaphors. But this is not valid, because a metaphor is interpreted according to something which is similar; whereas it does not follow, if something is similar in one respect, that it is similar in all respects.
Lecture 17
How to investigate the why in special problems; how certain problems agree as to propter quid, either because their middles have a kind of unity or are subordinated
a1. In order to formulate the connexions we wish to prove we have to select our analyses and divisions. The method of selection consists in laying down the common genus of all our subjects of investigation — if e.g., they are animals, we lay down what the properties are which inhere in every animal. These established, we next lay down the properties essentially connected with the first of the remaining classes—e.g., if this first subgenus is bird, the essential properties of every bird—and so on, always characterizing the proximate subgenus. This will clearly at once enable us to say in virtue of what character the subgenera—man, e.g., or horse—possess their properties. Let A be animal, B the properties of every animal, C D E various species of animal. Then it is clear in virtue of what character B inheres in D—namely A—and that it inheres in C and E for the same reason: and throughout the remaining subgenera always the same rule applies.
a13. We are now taking our examples from the traditional class-names, but we must not confine ourselves to considering these. We must collect any other common character which we observe, and then consider with what species it is connected and what properties belong to it. For example, as the common properties of horned animals we collect the possession of a third stomach and only one row of teeth. Then since it is clear in virtue of what character they possess these attributes—namely their horned character—the next question is, to what species does the possession of horns attach?
a20. Yet a further method of selection is by analogy: for we cannot find a single identical name to give to a squid’s pounce, a fish’s spine, and an animal’s bone, although these too possess common properties as if there were a single osseous nature.
a23. Some connexions that require proof are identical in that they possess an identical ‘middle’ e.g., a whole group might be proved through ‘reciprocal replacement’ — and of these one class are identical in genus, namely all those whose difference consists in their concerning different subjects or in their mode of manifestation. This latter class may be exemplified by the questions as to the causes respectively of echo, of reflection, and of the rainbow: the connexions to be proved which these questions embody are identical generically, because all three are forms of repercussion; but specifically they are different.
a29. Other connexions that require proof only differ in that the ‘middle’ of the one is subordinate to the ‘middle’ of the other. For example: Why does the Nile rise towards the end of the month? Because towards its close the month is more stormy. Why is the month more stormy towards its close? Because the moon is waning. Here the one cause is subordinate to the other.
In order to formulate the connexions. After showing how one should go about investigating the 'quod quid', the Philosopher now shows how one should investigate 'propter quid'.
Concerning this he does two things.
First, he shows how 'propter quid' should be investigated.
Second, how diverse questions make use of a common 'propter quid', at: the question might be raised (99a35; [566]).
Concerning the first he does two things.
First, he shows that one takes the 'propter quid' by taking some common univocal item.
Second, by taking some common analogous item, at: some connexions that require proof (99a23; [564]).
Concerning the first he does two things.
First, he teaches how to take the propter quid by taking a common univocal item which is a definitively named genus.
Second, by taking anything else that is common, at: we are now taking our examples (99a13; [562]).
He says therefore first (99a1) that in order to get the 'propter quid' in regard to individual problems that are proposed, it is required to consider divisions and subdivisions, and thus to proceed to the individual cases by disputing, having first supposed a common genus. For example, if someone wished to consider why something belongs to certain types of animals, he would have to discover what items belong to every animal. Once these have been discovered, he would once more consult the divisions to determine what things follow first upon that common item which is contained under animal; for example, what things follow upon every bird. Then one would continue in this manner, always taking the first item into which a given division is immediately divided. (This is the very thing that was observed above in the divisions by which one proceeds to investigate 'quod quid'). By thus proceeding it is obvious that we shall always be able to say 'propter quid' certain things are present in those things which are contained under something common.
Thus, if we would like to know 'why' certain things such as being asleep and being awake are found in man and horse, we would let animal be that in which A, the middle, is found, and let B, that is, the major extreme, stand for items that inhere in every animal, say, being asleep and awake. Then we let certain species of animals, such as man, horse, cow, be taken as minor extremes, namely, C, D, E. In this way it is manifest that the reason 'why' B, that is, being asleep or awake, is found in D, that is, in man, is that it is due to A, that is, because man is an animal. Then the same should be done in regard to the others, and the same notion must be observed in all.
The reason for this procedure is that the subject is the cause of a proper attribute. Therefore, if we wish to investigate the cause why some attribute is found in certain inferiors, it is necessary to take as common the proper subject through whose definition the cause of that attribute is taken.
Then, at: we are now taking our examples (99a13) he shows how to investigate the 'propter quid' by arriving at something common which is a genus without a definite name.
And he says that what has been stated above applies to those common items to which names have been assigned. However, it is not enough to consider only such items but also anything else which seems to be commonly present in them, even if it is not a genus or does not have a name. After that, one must discover what this common factor follows upon, as well as what follows upon this common unnamed factor. For example, to have horns is something common, but it neither has a name nor is it a genus. Furthermore, two things follow upon this common factor: one of these is that every horned animal, because it must chew its cud, has several stomachs; one of which, existing farther in and called echinus, is hard and prickly, as it is stated in The History of Animals II. Another item which follows upon horned animals is that they do not have teeth in both jaws, but only in the lower one, because the dental matter is converted into horns. Again one must consider which animals are apt to have horns, namely, cows and deers. For in that way it will be clear why these animals have those properties, namely, because they have horns.
Then, at: yet a further method of selection (99a20) he shows how to investigate 'propter quid' by arriving at some common analogous item.
And he says that another method of investigating 'propter quid' is to select something common according to analogy, that is, proportion. For it is possible to take something analogous which is not the same according to species or genus: for example, the bone (called sepion) of squid, the spine of fish and the backbone of land animals. For all these agree by proportion, because spine and backbone are related to fish and land animals in the same way. Now, because of this unity of proportion certain things follow upon this common analogous item, just as if they shared in one generic or specific nature; for example, to be covered with flesh.
Then, at: some connexions that require proof (99a23) he shows how many problems concur as to 'propter quid'.
First, as to having one middle.
Second, as to the order of the middles, at: other connexions that require proof (99a29; [565]).
He says therefore first (99a23) that some problems are the same, namely, inasmuch as they agree as to 'propter quid'. In one way, because they have the same middle: thus many things are demonstrated by the middle which is antiperistasis, that is, counter-resistance or reverberation. On the other hand, some middles are the same not absolutely but in genus, and these are diversified by certain differences which are based either on the diversity of subjects or on the diversity of their ways of coming to be. For example, if it is asked why an echo comes to be, or why something appears, namely, in a mirror, or why a rainbow is formed. For all these are the same problem as to the middle 'propter quid', which is generically the same, since all are caused by a reverberation. However, the reverberations differ specifically. For an echo comes to be through the reverberation of air set in motion by a sounding body toward a concave body; an image in a mirror comes to be by the fact that the modification of the medium is rebounded at the mirror; but the rainbow is formed by the rays of the sun being reflected back by moist vapors.
Then, at: other connexions that require proof (99a29) he shows how problems agree as to 'propter quid' by reason of the subordination of the middles.
And he says that there are certain other problems which differ from one another in point of having diverse middles, one of which is under another. And he gives the example that someone wonders why the Nile overflows more near the end of the month, that is, of the lunar month. For the reason is that there is more rain near the end of the month. And the reason for this is taken from another middle, namely, because the moon which controls moisture is waning then. Consequently, as its light wanes the vapors in the air condense more; and this causes rain. And so it is plain that those two middles are related to one another in the sense that one of them is under the other.