sarily in the subject. Now, as matter is the principle of individuation, the note of universality is effected on the abstraction of the form from determinate matter."
The conclusion to which St. Thomas has now led us is one which he develops with great skill and accuracy in elaborating the Aristotelian theory of the origin of knowledge, which he shows to include whatever fragments of truth are to be found in the various other systems that account for the origin of our ideas. He elsewhere (Sum. th., I, q. 9, a. 1) calls attention to the fact that "whatever changes is under one aspect permanent, though under another it is transient. Thus, when a body from being white becomes black, its substance remains, but its color [in the vulgar sense of the term] passes away." And this is true not of accidental form only, as in the example cited, but of substantial form also. For he tells us (Opusc. 27, De prin. nat.), "That which actuates substantial being is substantial form." He further argues (Quod. I, a. 6): "It is impossible that in one and the same entity there should be a plurality of substantial forms, for the reason that a thing derives its being and its unity from the same source. Now it is manifest that an entity receives its being through the form; wherefore, through the form likewise it receives its unity. Consequently, wherever there is a multitude of forms, the entity is not simply one." And again: "A form that is virtually more perfect contains within it the less perfect form. Therefore, the more perfect form supposed, it is superfluous to suppose the less perfect. Since, then, there is nothing superfluous in nature, nature does not suffer that in the same composite there should be two forms, one of which is more perfect than the other" (Opusc. 45, aliter 42). Hence "a form must be wholly spiritual or wholly unspiritual; though its faculties may be partly the one, partly the other. Neither [if the discussion be restricted to man] is it possible, for the same reason, that there should be a common ancestry, save in the analogical sense that the two classes of forms actuate the same primordial matter, and that the material organism exhibits a progressive development, in its gradual disposition
