Aquinas’ Commentary on Aristotle’s Posterior Analytics

By Jon|February 23, 2016|Commentary of Aquinas on The Posterior Analytics of Aristotle, Philosophy|

My Translation



Different colors are different premises.

Bold words were not known on first read.

Italics are questions

My Translation (for the purposes of studying)

[brackets] = implicit idea made explicit

[correction] = amendation to my translation.

Dominican English followed by Concept
Sicut dicit Aristoteles in principio metaphysicae, hominum genus arte et rationibus vivit: in quo videtur philosophus tangere quoddam hominis proprium quo a caeteris animalibus differt. Alia enim animalia quodam naturali instinctu ad suos actus aguntur; homo autem rationis iudicio in suis actionibus dirigitur. Et inde est quod ad actus humanos faciliter et ordinate perficiendos diversae artes deserviunt. Nihil enim aliud ars esse videtur, quam certa ordinatio rationis quomodo per determinata media ad debitum finem actus humani perveniant.


Just as Aristotle says in the beginning of the Metaphysics, the genus [race] of man lives in art and reasons: on which topic the philosopher seems to touch on a certain property of man, by which he differs from the rest of the animals. For other animals are driven to their acts by certain instincts of nature. But man is directed in his actions by judgment of reason. And thence [this is why] it is that diverse arts are devoted to performing the acts of man easily and methodically. For art seems to be nothing other than a certain ordering of human acts arriving to a due end through a determined material. [For art seems to be nothing more than a definite and fixed procedure established by reason, whereby human acts reach their due end through appropriate means.]

Definition of Art

As the Philosopher says in Metaphysics I (980b26), “the human race lives by art and reasonings.” In this statement the Philosopher seems to touch upon 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 ready and orderly performance of human acts. For an art seems to be nothing more than a definite and fixed procedure established by reason, whereby human acts reach their due end through appropriate means.


Ratio autem non solum dirigere potest inferiorum partium actus, sed etiam actus sui directiva est. Hoc enim est proprium intellectivae partis, ut in seipsam reflectatur: nam intellectus intelligit seipsum et similiter ratio de suo actu ratiocinari potest. Si igitur ex hoc, quod ratio de actu manus ratiocinatur, adinventa est ars aedificatoria vel fabrilis, per quas homo faciliter et ordinate huiusmodi actus exercere potest; eadem ratione ars quaedam necessaria est, quae sit directiva ipsius actus rationis, per quam scilicet homo in ipso actu rationis ordinate, faciliter et sine errore procedat.


The notion [reason] however is able not only to direct acts of inferior parts [powers], but also is directed by its acts [is director of its acts]. This also is proper to intellectual parts, as it is brought around in itself [ability to reflect upon itself]: for the intellect understands itself and similarly reason is able to reason about its own act. If therefore [it follows] from this, that [by the fact that] the reason reasoned about manual acts, the carpentry or building art, through which man is able to easily and methodically exercise various [manual] acts, was invented; likewise, a certain art by reason is necessary which is a directive of the act of reason-ing, namely through which man proceeds in its act of reason methodically, easily and without error.

The reason directs its own parts in reasoning.

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 carpentering, 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 when performing the act of reasoning might proceed in an orderly and easy manner and without error.
Et haec ars est logica, idest rationalis scientia. Quae non solum rationalis est ex hoc, quod est secundum rationem (quod est omnibus artibus commune); sed etiam ex hoc, quod est circa ipsum actum rationis sicut circa propriam materiam.


And this art is logic: the science of reason. Not only is “rational” taken from this [reason from this = regarding reason], because it is regarding reason (which is common to all arts); but also taken from this is the fact that it is about the very act of reason, just as it is about its proper matter.

Logic is according to reason, about the form of reasoning, and its matter.

And this art is logic, i.e., 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 with its proper matter.

quod – because, which, fact that

ex hoc – which is THIS. Purpose of this?

science or art?

quae –

Et ideo videtur esse ars artium, quia in actu rationis nos dirigit, a quo omnes artes procedunt. Oportet igitur logicae partes accipere secundum diversitatem actuum rationis.


And therefore it seems to be the art of arts, because we direct ourselves in acts of reasoning, from which all arts proceed. It is necessary therefore to grasp the parts of logic according to a diversity of acts of reason.

We need to understand the various acts of reason.

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.
Sunt autem rationis tres actus: quorum primi duo sunt rationis, secundum quod est intellectus quidam. Una enim actio intellectus est intelligentia indivisibilium sive incomplexorum, secundum quam concipit quid est res. Et haec operatio a quibusdam dicitur informatio intellectus sive imaginatio per intellectum. Et ad hanc operationem rationis ordinatur doctrina, quam tradit Aristoteles in libro praedicamentorum. Secunda vero operatio intellectus est compositio vel divisio intellectus, in qua est iam verum vel falsum. Et huic rationis actui deservit doctrina, quam tradit Aristoteles in libro perihermeneias. Tertius vero actus rationis est secundum id quod est proprium rationis, scilicet discurrere ab uno in aliud, ut per id quod est notum deveniat in cognitionem ignoti. Et huic actui deserviunt reliqui libri logicae. But there are three acts of the reason, of which the first two are of reason, insofar as it is of the intellect. For one act of the intellect is the understanding of things indivisible or uncomplex, insofar as what [according to which] it conceives what a thing is. And this operation is named by a certain [by some the] informing of the intellect or [the] imagination through the intellect. And to this operation of reason is ordered [the] doctrine, which Aristotle handed on in the book “Predicaments/Categories” But the second operation of the intellect is composition or division of understanding, in which there is now [found for the first time] truth or falsity. And for this act of reason the doctrine was guarded [is considered], which Aristotle handed on in the book “On Interpretation.” But the third act of reason is according to that which is proper to the reason, namely to regress from one to another, in order that, through that which is known, it might reach into the knowledge of the unknown. And to this act serves [is considered] the rest of the book of logic.

Three operations of the intellect

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. And 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 ordained the doctrine which Aristotle hands down in the book of Predicaments, [i.e., 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 doctrine 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.
Attendendum est autem quod actus rationis similes sunt, quantum ad aliquid, actibus naturae. Unde et ars imitatur naturam in quantum potest. In actibus autem naturae invenitur triplex diversitas. In quibusdam enim natura ex necessitate agit, ita quod non potest deficere. In quibusdam vero natura ut frequentius operatur, licet quandoque (interdum) possit deficere a proprio actu. Unde in his necesse est esse duplicem actum; unum, qui sit ut in pluribus, sicut cum ex semine generatur animal perfectum; alium vero quando natura deficit ab eo quod est sibi conveniens, sicut cum ex semine generatur aliquod monstrum propter corruptionem alicuius principii. But it should be noted that the acts of reason are similar, [in a certain sense, to] as much as to another, by acts of nature. Whence even art imitates nature inasmuch as it can. In acts of nature a threefold diversity is found, for in certain subjects, nature works from necessity, so that it is not able to fail. But in certain [other] subjects nature works as frequently [for the most part], although sometimes it is able to fail from a proper act. Whence in this there needs to be two acts [a twofold act]; one, which is as in the many [in the majority of cases], just as when from seed a perfect animal is generated; the other when nature fails from this which is fitting to it, just as when from seed is generated some monster on account of corruption of some principle. 

Three way nature resolves itself: to necessarily perfect generation, for the most part and/or monsters.

It should be noted that the acts of reason are in a certain sense not unlike the acts of nature: hence so far as it can, art imitates nature. Now in the acts of nature we observe a threefold diversity. For in some of them nature acts from necessity, i.e., 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.
Et haec etiam tria inveniuntur in actibus rationis. Est enim aliquis rationis processus necessitatem inducens, in quo non est possibile esse veritatis defectum; et per huiusmodi rationis processum scientiae certitudo acquiritur. Est autem alius rationis processus, in quo ut in pluribus verum concluditur, non tamen necessitatem habens. Tertius vero rationis processus est, in quo ratio a vero deficit propter alicuius principii defectum; quod in ratiocinando erat observandum. And even these three are found in acts of reason. For there are some processes of reasons follow necessarily, in which it is not possible for there to be a defect of truth [where there is no possibly defect]; and through such a process of reason certainty of knowledge is acquired. But there is another process of reason, in which, as in the majority of cases [with the animals], truth is concluded [something true is concluded], not producing necessity. The third process of reason is that in which reason fails to obtain truth on account of some defect of principle; a fact that must have been [should have been] observed in reasoning.

Three results in nature applied to reasoning

These three are found also in the acts of the reason. For there is one process of reason which induces necessity, where it is not possible to fall short of the truth; and 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.
Pars autem logicae, quae primo deservit processui, pars iudicativa dicitur, eo quod iudicium est cum certitudine scientiae. Et quia iudicium certum de effectibus haberi non potest nisi resolvendo in prima principia, ideo pars haec analytica vocatur, idest resolutoria. Certitudo autem iudicii, quae per resolutionem habetur, est, vel ex ipsa forma syllogismi tantum, et ad hoc ordinatur liber priorum analyticorum, qui est de syllogismo simpliciter; vel etiam cum hoc ex materia, quia sumuntur propositiones per se et necessariae, et ad hoc ordinatur liber posteriorum analyticorum, qui est de syllogismo demonstrativo. The part of logic, which regards the first process is called the judicial part, because it is of a judgment [it leads to judgments] with certainty of science. And because certain judgments about effects are only able to be had by resolution [of them] in first principles, this part is called analysis [analytical], i.e. resolvent. But certainty of judgment, which is had through analysis, is [derived], either from only the form of the syllogism – and to this point is ordered the “Prior Analytics” which is about syllogisms most basically/simply; or with this [formal part] from matter, because propositions are taken [per se] and of necessity, and to this point the book “Posterior Analytics,” which is about the demonstrative syllogism.

First process of logic: produces certainty. Formal logic is dealt with in prior analytics and Material (implying formal too) logic is in posterior analytics.

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, i.e., resolvent. Furthermore, the certitude obtained by such an analysis of a judgment is derived either from the mere form of the syllogism—and to this is ordained 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 per se and necessary [cf. infra, Lectures 10, 13]—and to this is ordained the book of the Posterior Analytics which is concerned with the demonstrative syllogism.
Secundo autem rationis processui deservit alia pars logicae, quae dicitur inventiva. Nam inventio non semper est cum certitudine. Unde de his, quae inventa sunt, iudicium requiritur, ad hoc quod certitudo habeatur. Sicut autem in rebus naturalibus, in his quae ut in pluribus agunt, gradus quidam attenditur (quia quanto virtus naturae est fortior, tanto rarius deficit a suo effectu), ita et in processu rationis, qui non est cum omnimoda certitudine, gradus aliquis invenitur, secundum quod magis et minus ad perfectam certitudinem acceditur. Per huiusmodi enim processum, quandoque quidem, etsi non fiat scientia, fit tamen fides vel opinio propter probabilitatem propositionum, ex quibus proceditur: quia ratio totaliter declinat in unam partem contradictionis, licet cum formidine alterius, et ad hoc ordinatur topica sive dialectica. Nam syllogismus dialecticus ex probabilibus est, de quo agit Aristoteles in libro topicorum. But the other part of logic, which is called investigative is devoted to the second process of reason. For investigation is not always with certainty. Therefore, judgment is required about those things which were investigated, to that which [in order that] certainty may be had. But just as in natural things, in which are done as the in the majority of cases, a certain step accompanies (because as much as the strength of nature is stronger, so much more uncommon does its effect fail) So also in the process of reason, which is not with total certitude, some levels are found, according to inasmuch as one approaches to more or less perfect certitude. For through such a process, sometimes indeed, even though there might not be scientific knowledge, there comes to be nevertheless faith or opinion on account of a probable proposition, from which it came/started: because the reason leans to one side of contradition, althought with fear of the other. “The Topics” or “Dialectics are devoted to this. For a dialectical syllogism is provable, about which Aristotle treats in his book “The Topics.”

Second process of logic: Less certain knowledge – dealt with in the topics.


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 accordingly as one approaches more or less to complete certitude. For 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 fear concerning 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.
Quandoque vero, non fit complete fides vel opinio, sed suspicio quaedam, quia non totaliter declinatur ad unam partem contradictionis, licet magis inclinetur in hanc quam in illam. Et ad hoc ordinatur rhetorica. Quandoque vero sola existimatio declinat in aliquam partem contradictionis propter aliquam repraesentationem, ad modum quo fit homini abominatio alicuius cibi, si repraesentetur ei sub similitudine alicuius abominabilis. Et ad hoc ordinatur poetica; nam poetae est inducere ad aliquod virtuosum per aliquam decentem repraesentationem. Omnia autem haec ad rationalem philosophiam pertinent: inducere enim ex uno in aliud rationis est. But sometimes, faith [belief] or opinion does not come to be [is not achieved] fully, but rather a certain suspicion, because [reason] is not totally leaned away to one part of contradiction, although it was leaning in one more than another. And to this type Rhetoric is ordained. But sometimes only opinion [de]clines one to some part of contradiction on account of some similarity, as much [much like] as that by which a man becomes averted from some food, if it is represented to him under the likeness of a certain aversion. And to this Poetics is ordered; for it belongs to poets to induce [us] to something virtuous through some decent/fitting/appropriate representation. But all this pertains to philosophical reasoning: for to lead from one thing to another belongs to the reason.

Still second process of logic?: failed or [non] logical arts.

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 the reason, for it belongs to reason to pass from one thing to another.
Tertio autem processui rationis deservit pars logicae, quae dicitur sophistica, de qua agit Aristoteles in libro elenchorum. But the part of logic, which is called sophistry – and about which Aristotle treats in his book “On Sophistical Refutations”, serves the third process of reason. 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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