Commentary Aristotle Posterior Analytics
Commentary on the Posterior Analytics
Book 1. The Demonstrative Syllogism
Lecture 1. The Need for Preexistent Knowledge in All Learning
71a1. All instruction given or received by way of argument proceeds from preexistent knowledge. This becomes evident upon a survey of all the species of such instruction.
71a3. The mathematical sciences and all other speculative disciplines are acquired in this way.
71a4. And so are the two forms of dialectical reasoning, syllogistic and inductive, for each of these latter make use of old knowledge to impart new. The syllogism assumes an audience that accepts its premises; induction exhibits the universal as implicit in the clearly known particular.
71a9. Again, the persuasion exerted by rhetorical arguments is in principle the same, since they use either example (a kind of induction) or enthymeme (a form of syllogism).
As the Philosopher says in Metaphysics 1.980b26: the human race lives by art and reasonings. In this statement, the Philosopher seems to touch on that property whereby man differs from the other animals. For the other animals are prompted to their acts by a natural impulse, but man is directed in his actions by a judgment of reason. And this is the reason why there are various arts devoted to the easy and orderly performance of human acts. For an art seems to be nothing more than a definite and fixed procedure established by reason, by which human acts reach their due end through appropriate means. Now, reason is not only able to direct the acts of the lower powers, but is also director of its own act, for what is peculiar to the intellective part of man is its ability to reflect upon itself; for the intellect knows itself. In like manner, reason is able to reason about its own act. Therefore, just as the art of building or carpentry, through which man is enabled to perform manual acts in an easy and orderly manner, arose from the fact that reason reasoned about manual acts, so in like manner an art is needed to direct the act of reasoning, so that by it a man might proceed in an orderly and easy manner and without error when performing the act of reasoning.
And this art is logic, or the science of reason. And it concerns reason not only because it is according to reason, for that is common to all arts, but also because it is concerned with the very act of reasoning as its proper matter.
Therefore, it seems to be the art of the arts, because it directs us in the act of reasoning, from which all arts proceed. Consequently, one should view the parts of logic according to the diversity among the acts of reason.
Now, there are three acts of the reason, the first two of which belong to reason regarded as an intellect. One action of the intellect is the understanding of indivisible or uncomplex things, and according to this action it conceives what a thing is. This operation is called by some the “informing of the intellect,” or “representing by means of the intellect.” To this operation of the reason is ordered the teaching which Aristotle hands down in the book of Categories.
The second operation of the intellect is its act of combining or dividing, in which the true or the false are for the first time present. And this act of reason is the subject of the teaching which Aristotle hands down in the book entitled On Interpretation.
But the third act of the reason is concerned with that which is peculiar to reason, namely, to advance from one thing to another in such a way that through that which is known a man comes to a knowledge of the unknown. And this act is considered in the remaining books of logic.
It should be noted that the acts of reason are in a certain sense not unlike the acts of nature. Thus, art imitates nature as far as it is able. Now, in the acts of nature we observe a threefold diversity.
For in some of them nature acts from necessity, namely, in such a way that it cannot fail;
in others, nature acts so as to succeed for the most part, although now and then it fails in its act.
Hence in this latter case there must be a twofold act:
one which succeeds in the majority of cases, as when from seed is generated a perfect animal;
the other when nature fails in regard to what is appropriate to it, as when from seed something monstrous is generated owing to a defect in some principle.
These three are found also in the acts of the reason.
For there is one process of reason which induces necessity, in which it is not possible to fall short of the truth. By such a process of reasoning, the certainty of science is acquired.
Again, there is a process of reason in which something true in most cases is concluded, but without producing necessity.
But the third process of reason is that in which reason fails to reach a truth because some principle which should have been observed in reasoning was defective.
Now, the part of logic which is devoted to the first process is called the judicative part, because it leads to judgments possessed of the certitude of science. And because a certain and sure judgment touching effects cannot be obtained except by analyzing them into their first principles, this part is called analytical, or resolvent. Now, the certitude obtained by such an analysis of a judgment is derived either from the mere form of the syllogism—and to this is ordered the book of the Prior Analytics, which treats of the syllogism as such—or from the matter along with the form, because the propositions employed are essential and necessary—and to this is ordered the book of the Posterior Analytics, which is concerned with the demonstrative syllogism.
To the second process of reason, another part of logic, called investigative, is devoted. For investigation is not always accompanied by certitude. Hence in order to have certitude, a judgment must be formed, bearing on that which has been investigated. But just as in the works of nature, which succeed in the majority of cases, certain levels are achieved—because the stronger the power of nature, the more rarely does it fail to achieve its effect—so too in that process of reason which is not accompanied by complete certitude, certain levels are found according to how close one approaches to complete certitude.
Although science is not obtained by this process of reason, nevertheless belief or opinion is sometimes achieved (on account of the provability of the propositions one starts with), because reason leans completely to one side of a contradiction, but with trepidation about the other side. The Topics, or dialectics, is devoted to this. For the dialectical syllogism which Aristotle treats in the book of Topics proceeds from premises which are provable.
At times, however, belief or opinion is not altogether achieved, but suspicion is, because reason does not lean to one side of a contradiction unreservedly, although it is inclined more to one side than to the other. To this the Rhetoric is devoted.
At other times, a mere fancy inclines one to one side of a contradiction because of some representation, much as a man turns in disgust from certain food if it is described to him in terms of something disgusting. And to this is ordained the Poetics. For the poet’s task is to lead us to something virtuous by some excellent description.
And all these pertain to the philosophy of reason, for it belongs to reason to pass from one thing to another.
The third process of reasoning is served by that part of logic which is called sophistry, which Aristotle treats in the book On Sophistical Refutations.
Leaving aside the other parts of logic, we shall fix our attention on the judicative part as it is presented in the book of Posterior Analytics, which is divided into two parts.
In the first, he shows the need for the demonstrative syllogism, with which this book is concerned.
In the second part he comes to a decision concerning that syllogism: we suppose ourselves (71b8; [28]).
Now the need for anything directed to an end is caused by that end. But the end of the demonstrative syllogism is the attainment of science. Hence if science could not be achieved by syllogizing or arguing, there would be no need for the demonstrative syllogism.
Plato, as a matter of fact, held that science in us is not the result of a syllogism but of an impression upon our minds of ideal forms from which, he said, are also derived the natural forms in natural things, which he supposed were participations of forms separated from matter. From this it followed that natural agents were not the causes of forms in natural things, but merely prepared the matter for participating in the separated forms. In like fashion, he postulated that science in us is not caused by study and training, but only that obstacles are removed, and man is brought to recall things which he naturally understands in virtue of an imprint of separated forms.
But Aristotle’s view is opposed to this on two counts.
For he maintains that natural forms are made actual by forms present in matter, that is, by the forms of natural agents.
He further maintains that science is made actual in us by other knowledge already existing in us. This means that it is formed in us through a syllogism or some type of argument. For in arguing we proceed from one thing into another.
Therefore, in order to show the need for demonstrative syllogism, Aristotle begins by stating that some of our knowledge is acquired from knowledge already existing.
Therefore, he does two things:
first, he states his thesis;
second, he explains the character of prior knowledge, at: the preexistent knowledge (71a11; [13]).
Concerning the first he does two things.
First (71a1), he asserts a universal proposition containing his thesis, namely, that the production of knowledge in us is caused from knowledge already existing. Hence he says: every doctrine and every discipline. He does not say, “all knowledge,” because not all knowledge depends on previous knowledge (for that would involve an infinite process), but the acquisition of every discipline comes from knowledge already possessed.
For the names “doctrine” and “discipline” pertain to the learning process, doctrine being the action exerted by the one who makes us know, and discipline the reception of knowledge from another.
Furthermore, “doctrine” and “discipline” are not taken here as pertaining only to the acquisition of scientific knowledge, but to the acquiring of any knowledge. That this is so is evident because he explains the proposition even in regard to dialectical and rhetorical disputations, neither of which engenders science. Hence this is another reason why he did not say, from preexistent “science” or “intuition,” but knowledge universally.
However, he does add intellectual, in order to preclude knowledge acquired by sense or imagination. For reason alone proceeds from one thing into another.
Then, at: the mathematical sciences (71a3), he employs induction to prove his thesis.
First, he does this in regard to those demonstrations in which scientific knowledge is acquired. Of these, the best are the mathematical sciences, because of their most certain manner of demonstrating. After them come the other arts, because some manner of demonstrating is found in all of them; otherwise, they would not be sciences.
Second, at and so are the two forms (71a4), he proves the same thing in regard to disputative (that is, dialectical) arguments, because they employ syllogism and induction, in each of which the process starts from something already known. For in a syllogism, the knowledge of some universal conclusion is obtained from other universals already known; in induction, however, a universal is concluded from singulars made known in sense-perception.
Third, at again, the persuasion (71a9), he manifests the same thing in rhetorical arguments, in which persuasion is produced through an enthymeme or example, but not through a syllogism or complete induction because of the uncertainty attending the matters discussed—namely, the individual acts of men in which universal propositions cannot be truthfully assumed. Therefore, in place of a syllogism, in which there must be something universal, an enthymeme is employed, in which it is not necessary to have something universal. Similarly, in place of induction, in which a universal is concluded, an example is employed in which one goes from the singular to the singular, and not to the universal. Thus it is clear that just as the enthymeme is an abridged syllogism, so an example is an incomplete induction. Therefore, if in the case of the syllogism and induction one proceeds from knowledge already existing, the same must be granted in the case of the enthymeme and example.