Analytics – Aristotle

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Commentary on the Posterior Analytics of Aristotle
St. Thomas Aquinas (translated by Fabian R. Larcher, O.P.)
Foreword (of St. Thomas Aquinas)
As the Philosopher says in Metaphysics I (980b26), “the human
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
race lives by art and reasonings.” In this statement the Philosopher
understanding of indivisible or uncomplex things and according to this
seems to touch upon that property whereby man differs from the other
action it conceives what a thing is. And this operation is called by some
animals. For the other animals are prompted to their acts by a natural
the informing of the intellect, or representing by means of the intellect.
impulse, but man is directed in his actions by judgment of reason. And
To this operation of the reason is ordained the doctrine which Aristotle
this is the reason why there are various arts devoted to the ready and
hands down in the book of Predicaments, [i.e., Categories]. The second
orderly performance of human acts. For an art seems to be nothing more
operation of the intellect is its act of combining or dividing, in which the
than a definite and fixed procedure established by reason, whereby
true or the false are for the first time present. And this act of reason is the
human acts reach their due end through appropriate means.
subject of the doctrine which Aristotle hands down in the book entitled
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 jus as the art of building or carpentering, through which man
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 s known a man comes to a
knowledge of the unknown. And this act is concerned in the remaining
books of logic.
is enabled to perform manual acts in an easy and orderly manner, arose
It should be noted that the acts of reason are in a certain sense
from the fact that reason reasoned about manual acts, so in like manner
not unlike the acts of nature: hence so far as it can, art imitates nature.
an art is need to direct the act of reasoning, so that by it a man when
Now in the acts of nature we observe a threefold diversity. For in some of
performing the act of reasoning might proceed in an orderly and easy
them nature acts from necessity, i.e., in such a way that it cannot fail; in
manner and without error. And this art is logic, i.e., the science of reason.
others, nature acts so as to succeed for the most part, although now and
And it concerns reason not only because it is according to reason, for that
then it fails in its act. Hence in this latter case there must be a twofold act:
is common to all arts, but also because it is concerned with the very act of
one which succeeds in the majority of cases, as when from seed is
reasoning as with its proper matter. Therefore it seems to be the art or
generated a perfect animal; the other when nature fails in regard to what
the arts, because it directs us in the act of reasoning, from which all arts
is appropriate to it, as when from seed something monstrous is
proceed.
generated owing to a defect in some principle.
These three are found also in the acts of the reason. For there is
accordingly as one approaches more or less to complete certitude. For
one process of reason which induces necessity, where it is not possible to
although science is not obtained by this process of reason, nevertheless
fall short of the truth; and but such a process of reasoning the certainty of
belief or opinion is sometimes achieved (on account of the probability of
science is acquired. Again, there is a process of reason in which
the propositions one starts with), because reason leans completely to
something true in most cases is concluded but without producing
one side of a contradiction but with fear concerning the other side. The
necessity. But the third process of reason is that in which reason fails to
Topics or dialectics is devoted to this. For the dialectical syllogism which
reach a truth because some principle which should have been observed
Aristotle treats in the book of Topics proceeds from premises which are
in reasoning was defective.
provable.
Now the part of logic which is devoted to the first process is
At times, however, belief or opinion is not altogether achieved,
called the judicative part, because it leads to judgments possessed of the
but suspicion is, because reason does not lean to one side of a
certitude of science. And because a certain and sure judgment touching
contradiction unreservedly, although it is inclined more to one side than
effects cannot be obtained except by analyzing them into their first
to the other. To this the Rhetoric is devoted. At other times a mere fancy
principles, this part is called analytical, i.e., resolvent. Furthermore, the
inclines one to one side of a contradiction because of some
certitude obtained by such an analysis of a judgment is derived either
representation, much as a man turns in disgust from certain food if it is
from the mere form of the syllogism—and to this is ordained the book of
described to him in terms of something disgusting. And to this is
the Prior Analytics which treats of the syllogism as such—or from the
ordained the Poetics. For the poet’s task is to lead us to something
matter along with the form, because the propositions employed are per
virtuous by some excellent description. And all these pertain to the
se and necessary [cf. infra, Lectures 10, 13]—and to this is ordained the
philosophy of the reason, for it belongs to reason to pass from one thing
book of the Posterior Analytics which is concerned with the
to another.
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
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.
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