Commentary Aristotle Posterior Analytics
Book 2
The Principles of the Demonstrative Syllogism
Lecture 1
Each of the four questions which pertain to science is one way or another a question of the middle b21. The kinds of question we ask are as many as the kinds of things which we know. They are in fact four: (1) whether the connexion of an attribute with a thing is a fact, (2) what is the reason of the connexion, (3) whether a thing exists, (4) What is the nature of the thing.
b26. Thus, when our question concerns a complex of thing and attribute and we ask whether the thing is thus or otherwise qualified — whether, e.g., the sun suffers eclipse or not — then we are asking as to the fact of a connexion. That our inquiry ceases with the discovery that the sun does suffer eclipse is an indication of this; and if we know from the start that the sun suffers eclipse, we do not inquire whether it does so or not.
b28. On the other hand, when we know the fact we ask the reason; as, for example, when we know that the sun is being eclipsed and that an earthquake is in progress, it is the reason of eclipse or earthquake into which we inquire. Where a complex is concerned, then, those are the two questions we ask;
b32. but for some objects of inquiry we have a different kind of question to ask, such as whether there is or is not a centaur or a God. (By ‘is or is not’ I mean ‘is or is not, without further qualification’; as opposed to ‘is or is not [e.g.] white’.) On the other hand, when we have ascertained the thing’s existence, we inquire as to its nature, asking, for instance, ‘what, then, is God?’ or ‘what is man?’. These, then, are the four kinds of question we ask, and it is in the answers to these questions that our knowledge consists.
b38. Now, when we ask whether a connexion is a fact, or whether a thing without qualification is, we are really asking whether the connexion or the thing has a ‘middle’; and when we have ascertained either that the connexion is a fact or that the thing is — that is, ascertained either the partial or the unqualified being of the thing—and are proceeding to ask the reason of the connexion or the nature of the thing, then we are asking what the ‘middle’ is.
a2. (By distinguishing the fact of the connexion and the existence of the thing as respectively the partial and the unqualified being of the thing, I mean that if we ask ‘does the moon suffer eclipse?’, or ‘does the moon wax?’, the question concerns a part of the thing’s being; for what we are asking in such questions is whether a thing is this or that, that is, has or has not this or that attribute: whereas, if we ask whether the moon or night exists, the question concerns the unqualified being of a thing.)
a5. We conclude that in all our inquiries we are asking either whether there is a ‘middle’ or what the ‘middle’ is: for the ‘middle’ here is precisely the cause, and it is the cause that we seek in all our inquiries. Thus, ‘Does the moon suffer eclipse?’ means ‘Is there or is there not a cause producing eclipse of the moon?’, and when we have learnt that there is, our next question is, ‘What, then, is this cause? for the cause through which a thing is — not is this or that, that is, has this or that attribute, but without qualification is — and the cause through which it is — not is without qualification, but is this or that as having some essential attribute or some accident — are both alike the middle’. By that which is without qualification I mean the subject, e.g., moon or earth or sun or triangle; by that which a subject is (in the partial sense) I mean a property, e.g., eclipse, equality or inequality, interposition or non-interposition. For in all these examples it is clear that the nature of the thing and the reason of the fact are identical: the question ‘What is eclipse?’ and its answer ‘The privation of the moon’s light by the interposition of the earth’ are identical with the question ‘What is the reason of eclipse?’ or ‘Why does the moon suffer eclipse?’ and the reply ‘Because of the failure of light through the earth’s shutting it out’. Again, for ‘What is a concord? A commensurate numerical ratio of a high and a low note’, we may substitute ‘What ratio makes a high and a low note concordant? Their relation according to a commensurate numerical ratio.’ ‘Are the high and the low note concordant?’ is equivalent to ‘Is their ratio commensurate?’; and when we find that it is commensurate, we ask ‘What, then, is their ratio?’.
Cases in which the ‘middle’ is sensible show that the object of our inquiry is always the ‘middle’: we inquire, because we have not perceived it, whether there is or is not a ‘middle’ causing, e.g., an eclipse. On the other hand, if we were on the moon we should not be inquiring either as to the fact or the reason, but both fact and reason would be obvious simultaneously. For the act of perception would have enabled us to know the universal too; since, the present fact of an eclipse being evident, perception would then at the same time give us the present fact of the earth’s screening the sun’s light, and from this would arise the universal. Thus, as we maintain, to know a thing’s nature is to know the reason why it is; and this is equally true of things in so far as they are said without qualification to be as opposed to being possessed of some attribute, and in so far as they are said to be possessed of some attribute such as equal to right angles, or greater or less.
It is clear, then, that all questions are a search for a ‘middle’.
The kinds of question. After determining about the demonstrative syllogism in the first book, the Philosopher intends in this [second] book to treat concerning its principles.
But there are two principles of the demonstrative syllogism, namely, its middle and the first indemonstrable propositions. Therefore, this book is divided into two parts.
In the first he determines concerning the knowledge of the middle in demonstrations.
In the second concerning the knowledge of the first propositions, at: as to the basic premises (100b18; [582]). For since it has been established in the first book that every doctrine and every discipline takes its start from preexisting knowledge, and since in demonstrations the knowledge of the conclusion is acquired through some middle and through the first indemonstrable propositions, we are left with the task of investigating how these come to be known.
But the first part is divided into two parts.
In the first he inquires what is a middle in demonstrations.
In the second part he inquires how that middle is made known to us, at: let us now state how essential nature (91a36; [418]).
But because the middle in demonstrations is employed in order to make known something about which there might have been doubt or question, therefore in regard to the first he does two things.
First, he lays down the number of questions.
Second, from these questions he pursues his investigation by showing how the questions pertain to the middle of demonstrations, at: now, when we ask (90b38; [412]).
Regarding the first he does three things.
First, he enumerates the questions.
Second, he explains complex questions, at: thus, when our question (90b26; [409]).
Third, simple questions, at: but for some objects (90b32; [411]).
He says therefore first (90b21) that the number of questions is equal to the number of things that are scientifically known. The reason for this is that science is knowledge acquired through demonstration. But things which we previously did not know are those of which we must seek knowledge by demonstration: for it is in regard to things which we do not know that we form questions. Hence it follows that the things we inquire about are equal in number to the things we know through science. But there are four things that we ask, namely, 'quia' [that is, is it a fact that], 'propter quid' [that is, why, or what is the cause or reason], 'si est' [if it is, that is, whether it is], 'quid est' [what is it]. To these four can be reduced whatever is scientifically inquirable or knowable. However in Topics I he divides questions or problems into four kinds in a different way, but all of them are included under one of the questions listed here, namely, the one called 'quia'. For in the Topics he is concerned only with questions to be disputed dialectically.