Expositio Libri Posteriorum
Commentary on the Posterior Analytics
De necessitate praecognitionis in omni doctrina et disciplina intellectiva
The Need for Preexistent Knowledge in All Learning
71a1. Omnis doctrina et omnis disciplina intellectiva ex praeexistenti fit cognitione. Manifestum est autem hoc speculantibus in omnes.
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. Mathematicae enim scientiarum per hunc modum fiunt et aliarum unaquaeque artium.
71a3. The mathematical sciences and all other speculative disciplines are acquired in this way.
71a5. Similiter autem et circa orationes quae per syllogismos et quae per inductionem; utraeque enim per prius nota faciunt doctrinam, hae quidem accipientes tanquam a notis, illae vero demonstrantes universale per id quod manifestum est singulare.
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. Similiter autem et rhetoricae persuadent; aut enim per exempla, quod est inductio, aut per enthymema, quod vere est syllogismus.
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).
1. 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 perveniatur. Ratio autem non solum dirigere potest inferiorum partium actus, sed etiam actus sui directiva est: hoc enim est proprium intellectivae partis ut in se ipsam reflectatur, nam intellectus intelligit se ipsum et similiter ratio de suo actu ratiocinari potest. Si igitur ex hoc quod ratio de actu manus ratiocinatur adinventa est ars aedificativa 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;
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.
2. et haec ars est logica, id est rationalis, scientia. Quae non solum rationalis est ex hoc quod est secundum rationem, quod est omnibus artibus commune, sed ex hoc quod est circa ipsum actum rationis sicut circa propriam materiam;
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.
3. 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.
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.
4. 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;
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.
secunda vero operatio intellectus est compositio vel divisio intellectuum, in qua est iam verum et falsum; et huic rationis actui deservit doctrina quam tradit Aristoteles in libro Perihermeneias.
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.
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 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.
5. 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:
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.
in quibusdam enim natura ex necessitate agit, ita quod non potest deficere;
For in some of them nature acts from necessity, namely, in such a way that it cannot fail;
in quibusdam vero natura ut frequentius operatur, licet quandoque et possit deficere a proprio actu,
in others, nature acts so as to succeed for the most part, although now and then it fails in its act.
unde in his necesse est esse duplicem actum:
Hence in this latter case there must be a twofold act:
unum qui sit ut in pluribus, sicut cum ex semine generatur animal perfectum,
one which succeeds in the majority of cases, as when from seed is generated a perfect animal;
alium vero quando natura deficit ab eo quod est sibi conveniens, sicut cum ex semine generatur aliquod monstrum, propter corruptionem alicuius principii.
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:
These three are found also in the acts of the reason.
est enim aliquis rationis processus necessitatem inducens, in quo non est possibile esse veritatis defectum, et per huiusmodi rationis processum scientiae certitudo acquiritur;
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.
est autem alius rationis processus in quo ut in pluribus verum concluditur, non tamen necessitatem habens;
Again, there is a process of reason in which something true in most cases is concluded, but without producing necessity.
tertius vero rationis processus est in quo ratio a vero deficit, propter alicuius principii defectum quod in ratiocinando erat observandum.
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.
6. 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, pars haec analectica vocatur, id est resolutoria. Certitudo autem iudicii quae per resolutionem habetur est vel ex ipsa forma syllogismi tantum, et ad hoc ordinatur liber Priorum analecticorum, qui est de syllogismo simpliciter, vel etiam cum hoc ex materia, quia sumuntur propositiones per se et necessariae, et ad hoc ordinatur liber Posteriorum Analecticorum, qui est de syllogismo demonstrativo.
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.
Secundo autem rationis processui deservit alia pars logicae quae dicitur inventiva: nam inventio non semper cum certitudine est, 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.
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.
—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 Aristotiles in libro Topicorum.
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.
—Quandoque vero non fit completae 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.
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.
—Quandoque vero sola estimatio declinat in aliquam partem contradictionis propter aliquam representationem, ad modum quo fit homini abhominatio alicuius cibi si representetur ei sub similitudine alicuius abhominabilis; et ad hoc ordinatur Poetica, nam poetae est inducere ad aliquid virtuosum per aliquam virtuosum per aliquam decentem representationem.
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.
—Omnia autem haec ad rationalem philosophiam pertinent: inducere enim ex uno in aliud rationis est.
And all these pertain to the philosophy of 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.
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.
7. Aliis igitur partibus logicae praetermissis, ad praesens intendendum est circa partem iudicativam, prout traditur in libro Posteriorum Analyticorum.
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.
Qui dividitur in partes duas: in prima ostendit necessitatem demonstrativi syllogismi, de quo est iste liber;
In the first, he shows the need for the demonstrative syllogism, with which this book is concerned.
in secunda de ipso syllogismo demonstrativo determinat, ibi: scire autem opinamur etc.
In the second part he comes to a decision concerning that syllogism: we suppose ourselves (71b8; ).
8. Necessitas autem cuiuslibet rei ordinatae ad finem ex suo fine sumitur; finis autem demonstrativi syllogismi est acquisitio scientiae; unde, si scientia acquiri non posset per syllogismum vel argumentum, nulla esset necessitas demonstrativi syllogismi. Posuit autem Plato quod scientia in nobis non causatur ex syllogismo, sed ex impressione formarum idealium in animas nostras, ex quibus etiam effluere dicebat formas materiales in rebus naturalibus, quas ponebat esse participationes quasdam formarum a materia separatarum; ex quo sequebatur quod agentia naturalia non causabant formas in rebus inferioribus, sed solum materiam praeparabant ad participandum formas separatas; et similiter ponebat quod per studium et exercitium non causatur in nobis scientia, sed tantum removentur impedimenta et reducitur homo quasi in memoriam eorum quae naturaliter scit ex impressione formarum separatarum.
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.
Sententia autem Aristotelis est contraria quantum ad utrumque:
But Aristotle’s view is opposed to this on two counts.