"A man's intellectual knowledge stands to his sensory knowledge as a sculptor chiselling an image out of marble stands to the workmen who bring the marble from the quarry. As the sculptor cannot exercise his art on the marble unless the workmen bring it to the quarry, so a man's intellect can form no ideas of sensible things unless it has presented to it through the external and internal senses sensible images of the same. But as the sculptor alone impresses in the marble brought him the idea of something conceived in his mind, so with his intellect alone does man form intellectual cognitions," -- i.e. universal concepts (Bödder, Psychologia, pp. 94, 95, translated). The intellect then (which must include the rational appetite, the will) is a free faculty, inorganic; chôristos at least in this sense, that it does not actualise any body organ, as sight actualises the eye; which led Aristotle to say that "were the eye an animal, sight would be its soul" (De anima, II, i, 9), as being its entelecheia, or form. But, it may be objected, from this it appears that the nous, or the intelligent soul, is not the form of the body. St Thomas would meet this grave objection by laying down, as he does (Sum. Theol., I, q. 77, a. 1), his distinction between the faculties and the essence (or substance) of the soul. This soul, he would say, is one substance, with faculties vegetative, sentient, and intelligent: it is the form of the body in respect of these vegetative and sentient faculties, and consequently in respect of the substance to which those faculties are attached, consequently also in respect even of the intelligent faculties, which are attached to the same substance of the soul. For this distinction of faculty and substance see Bödder, Psychologia, pp. 314, 315. The mediaeval mystics, as Thaulerus and Blosius, made much of this 'substance of the soul' (fundus animae, they called it), as distinct from the faculties: in this fundus animae, they declared, God dwells by grace as in His sanctuary, even when he is not actually thought of. It is the fashion now to rail at 'faculty psychology,' to scout the idea of 'substance,' to deny all 'potential being,' to allow of nothing but present actuality. Whoever is of that way of thinking, and takes up the Aristotelian idea of nous chôristos, need not be surprised to find himself carried further from St Thomas than Averroes and Alexander, even to the setting aside of the individual man altogether.
Of God and His Creatures: 2.68