The 'forms' here spoken of (not the human soul) are entities denoted by abstract names, as beauty, dexterity, squareness. They exist only in particular substances, and in each case imperfectly according to the imperfections of that in which they exist. Thus beauty is marred by the age, bodily infirmities and accidents, of any beautiful living being. No living being on earth is ideally beautiful. Is then every ideal 'form' something that practically cannot be? St Thomas thinks not. Recognising that the ideal cannot be except in a mind, he thereupon posits ideals which are themselves minds -- self-conscious ideals, and these are the angels. The Platonic ideas, or ideals, are thus brought into rerum natura as angels, one angel being the self-conscious ideal of one quality, as, perhaps, of swiftness, another of another, as, perhaps, of accuracy. Thus he says in II, 93: "Separate substances (i.e., angels) are certain essences existing by themselves (quidditates subsistentes)." This essence, existing by itself, and conscious of itself -- existing therefore in a mind, its own mind, as all ideal being needs to exist in a mind -- this ideal essence, I say, is not limited, as forms are limited in the material universe, by being reduced to the particular. An angel, says St Thomas (Contra Gent., 11, 93), is not reduced to the particular as one individual of many in a species: each angel is a species by himself, a living, conscious specific essence, sole of its kind. Thus among angels there are particular species, but not particular individuals of a species: this or that species is this or that individual, containing an ample measure, though not a divine fulness, of the specific essence. St Thomas does not say that specific forms necessarily exist by themselves: he does not teach the necessary existence of angels: all he argues is that, if these forms exist by themselves at all (si sint subsistentes), they must be self-conscious and intelligent beings. The utmost that he can be said to contend for is that angels are a fitting complement of the universe (II, 91). All that is absolutely necessary is the existence of a Supreme Being, who virtually contains in Himself all perfections which are represented in our minds by various abstract forms; a Being who is the Actuality of all ideal perfection (Chap. XXVIII).
The argument then in the text is: 'Imperfect forms are apparent everywhere in the material creation. Imperfect forms must come of perfect forms; perfect forms are ideal forms: ideal forms can exist nowhere but in the mind: if these ideal forms exist anywhere by themselves, they must themselves be minds conscious of what they are: such self-conscious ideals are the angels: anyhow, whether existing by themselves or not, ideals must be represented in one Perfect Mind: God therefore is Mind.' The argument is Platonic; or rather, Neoplatonist, as the making of the ideals into angels shows. It is rather a probable intuition than an argument. As an argument, it has many difficulties. St Thomas cannot have meant to say that any angel was living perfect beauty, or living perfect wisdom, for then it would be God: but perhaps we might have a living perfect fragrance, or a living perfect agility; and we may suppose that only these minor perfections, which do not carry all other perfections with them, are personified in the angels, and that only in an imperfect way.
Omitting the theory of angels, which will recur again (Book II, Chap. LV, XCVIII, with notes) we may formulate the matter finally thus: The ideal must be realised somewhere. It is realisable only in mind. Now whatever we may think of angels, and their intermediate realisation of ideals, we must arrive ultimately at one mind that realises the whole ideal order. That one grand realiser and realisation of all ideals is the Mind of God.
Of God and His Creatures: 1.44