St Thomas may have seen Greek MSS. of Aristotle in Italy, or at Paris, but I doubt if he could read them for himself. He is dependent on Latin translations, often bad ones. See an example in my Aquinas Ethicus, I, p. 111. In his Opusculum de Unitate Intellectus, he mentions his having seen a thirteenth and fourteenth book of Aristotle's Metaphysics, but declines further reference to them as being "not yet translated into our tongue." St Thomas and the mediaeval architects had genius, the fruits of which we still admire: but they had not at hand the manifold adminicula of the modern builder and the modern scholar. Nor was Averroes and the Arabian school any better off for Greek than St Thomas (Renan, p. 48).
To this particular explanation of Aristotle however the Commentator would have been at no loss for a reply. The Greek referred to is De anima, II, i, 6, 8. Aristotle adds (n. 12), after saying that some parts of the soul are not separable from the body: "There is nothing to prevent some parts of the soul being separable from the body, because they are actualisations of nothing corporeal." A conclusion seems to follow, the very opposite of that which St Thomas draws, and exactly what Averroes wishes, namely, that the intellectual part of the soul is not the actualisation, or form, of anything corporeal, but dwells apart from all body. In the above quoted Opusculum, 'De unitate intellectus contra Averroistas, which I take to be a later production, St Thomas recognises the force of this reply, and re-adjusts his position thus: "The intellect is a faculty of the soul, and the soul is the form of the body: but the power that is called intellect is not the actualisation of any bodily organ, because the activity of the body has nothing in common with the activity of intellect." Intellectus est potentia animae, quae est corporis forma, licet ipsa potentia, quae est intellectus, non est alicujus organi actus, quia nihil ipsius operationi communicat corporis operatio (De unitate intellectus, cap. iii). So also Chap. LXVIII, last paragraph, and in Chap. LXIX (already translated) the replies nn. 3, 4, p. 117.
ln this later explanation St Thomas has the support of Averroes, who says (De anima, III, p. 149): "But it has not been shown whether the body is perfected (or actualised) in the same way by all the powers of the soul; or whether there be some one of those powers whereby the body is not perfected (actualised, or informed)." I am persuaded that the retention of the paragraph as it stands in the text was due to an oversight on the part of the author. See note on p. 99 [i.e., note e in Chapter XXXII].
Of God and His Creatures: 2.61