The Significance of Ousia

I'll give here the argument I mentioned in the previous post.

According to Aquinas, Aristotle begins Z by invoking the categories (or so one may speak, if one reads De Ente et Essentia, as I have suggested, as a brief commentary on Met. Z and L), in accordance with the strategy of beginning with what is 'more knowable' by us. Aquinas suggests that the behavior of the predicate o)/n, as shown in the ramification of its uses into the various categories, is more knowable than the behavior of ou)si/a:

Quia vero ex compositis simplicium cognitionem accipere debemus et ex posterioribus in priora devenire, ut, a facilioribus incipientes, convenientior fiat disciplina, ideo ex significatione entis ad significationem essentiae procedendum est.

But then, according to Aquinas, Aristotle uses the fact of the categories, as the basis for an argument about the signficance of ou)si/a. Here is his extremely economical presentation of the argument:

(*) Et quia, ut dictum est, ens hoc modo dictum dividitur per decem genera, oportet quod essentia significet aliquid commune omnibus naturis, per quas diversa entia in diversis generibus et speciebus collocantur, sicut humanitas est essentia hominis, et sic de aliis.

Aquinas then mentions various near equivalents, as he sees it, of essentia, namely, quiditas, quod quid erat esse, forma, natura:

Et quia illud, per quod res constituitur in proprio genere vel specie, est hoc quod significatur per diffinitionem indicantem quid est res, inde est quod nomen essentiae a philosophis in nomen quiditatis mutatur.

Et hoc est quod philosophus frequenter nominat quod quid erat esse, id est hoc per quod aliquid habet esse quid.

Dicitur etiam forma secundum quod per formam significatur certitudo uniuscuiusque rei, ut dicit Avicenna in II metaphysicae suae.

Hoc etiam alio nomine natura dicitur accipiendo naturam secundum primum modum illorum quattuor, quos Boethius in libro de duabus naturis assignat, secundum scilicet quod natura dicitur omne illud quod intellectu quoquo modo capi potest. Non enim res est intelligibilis nisi per diffinitionem et essentiam suam. Et sic etiam philosophus dicit in V metaphysicae quod omnis substantia est natura.

These then gets fairly naturally connected with 'definition':

Quiditatis vero nomen sumitur ex hoc, quod per diffinitionem significatur.

And it can be seen that Aquinas thereby wishes to explain which topics get covered in Z.

But what especially interests me is the argument (*) above. It seems to be something like:

1. The various predications of 'is' correspond to the highest sorts.
2. Thus, what is signified by 'is' is that which makes something such that it can be sorted (at all).
3. Ousia is what is signified by 'is'.
4. Thus, ousia is that which makes something such that it can be sorted.
   

Met. Z then becomes an investigation of what it is by which things are sorted; the above account explains why, in light of this, it deals with the topics it does; 'matter' (hule) would get brought in insofar as it is relevant to sorting something; and genos and katholou have to be dealt with, additionally, because they might look like they work in that way (What sorts something if not its genus--the very sort it belongs to?).

It may be seen that Aquinas does not take Z1's appeal to the categories, as does Burnyeat, to be a restriction of our attention to the first category: he thinks that the question, 'What is it which makes this such that it can be sorted?', may be asked of a thing in any category, although, to be sure, it is most properly asked of things in the first category.

Let me underline a point: argument (*) seems to me one of the more startling, interesting, and (if correct) important arguments I have encountered. I wonder if there is warrant in Z1 for ascribing it to Aristotle.