Aquinas Day By Day


Aquinas’s topic:  logic of arguments: why demonstrative arguments are needed

Scripture: Aquinas’s text: Expositio libri Posteriorum , Bk. 1, lec. 1

Here Br. Thomas introduces the topics of scientific knowledge and demonstrative syllogisms by considering whether arguments are worthwhile at all.  He argues that arguments are indispensable by contrasting the views of Plato and Aristotle.  Typical of Aquinas’s approach, he draws an illuminating parallel in both philosophers between knowledge and reality.

Leaving aside the other parts of logic, our present attention concerns the judicative part of logic, as it is presented in the book of Posterior Analytics. It is divided into two parts. In the first, he shows the necessity of the demonstrative syllogism, with which this book is concerned; while in the second part he determines about the demonstrative syllogism.

Now the necessity of anything ordered to an end comes from that end. But the end of the demonstrative syllogism is acquiring scientific knowledge. Consequently, if it were not possible to acquire science by syllogism or argument, there would be no necessity for the demonstrative syllogism. Plato held that science in us is not caused by a syllogism but by the impression of ideal forms upon our souls.  And he said that from these forms also flow the natural forms in natural things, which he held were certain participations in forms separate from matter. From this it followed that natural agents do not cause the forms in inferior things, but merely prepare matter for participating in the separate forms. Likewise, he held that science in us is not caused by study and practice, but only that obstacles are removed and that a human is led back, as it were by recollection, to those things which he naturally understands from the impression of separate forms.

The view of Aristotle, however, is opposed to this on both counts. For he holds that natural forms are brought into actuality by forms that exist in matter, namely, by the forms of natural agents. Likewise, he holds that science actually comes to exist in us by means of some knowledge already present in us. This means that science comes about in us through a syllogism or some type of argument. For in arguing we proceed from one point to another.

Aliis igitur partibus logicae praetermissis, ad praesens intendendum est circa partem iudicativam, prout traditur in libro posteriorum analyticorum. Qui dividitur in partes duas: in prima, ostendit necessitatem demonstrativi syllogismi, de quo est iste liber; in secunda, de ipso syllogismo demonstrativo determinat; ibi: scire autem opinamur et cetera.

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 naturales 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.

Sententia autem Aristotelis est contraria quantum ad utrumque. Ponit enim quod formae naturales reducuntur in actum a formis quae sunt in materia, scilicet a formis naturalium agentium. Et similiter ponit quod scientia fit in nobis actu per aliquam scientiam in nobis praeexistentem. Et hoc est fieri in nobis scientiam per syllogismum aut argumentum quodcumque. Nam ex uno in aliud argumentando procedimus.

[Introductions and translations © R.E. Houser]