1. Origins of the Doctrine of Separation
Metaphysics, we have said, may also be understood as the science of what is utterly separate, or devoid of matter. Like many another doctrine in Greek thought, this one of separation, or distinguishing mind and matter, evolved gradually through a long line of philosophical thinkers. Its classical formulation in Aristotle represents, therefore, the efflorescence of an idea whose roots ran at least as far back as Anaxagoras, the first, or so it is commonly accepted, to put forth a separation, that is, distinction of mind from matter. It should be noted, however, that the Nous he proposes for meditation is not yet clearly differentiated from corporeal objects, nor is its influence on these objects sharply defined. Still, a first step was taken by him toward the separation from matter of an element of being that lay beyond matter.
With Plato the separation is decisive. The world of Ideas he postulated is a world of realities without so much as the shadow of matter attaching to them. For him, the Ideas were the necessary answer to the problem of intellectual knowledge. They alone, as he saw it, provided the intellect with the kind of object that could guarantee its knowledge, for they varied not at all but were permanent, and permanently self-identical. So that only knowledge pertaining to the Ideas deserved the name of science; all else was opinion, shifting and ephemeral. Plato, it may be said in passing, was quite correct as to the kind of object the intellect must have, but whether this object must exist in separation from matter, that is something else again.
Aristotle, for one, did not think so. Though agreeing that scientific knowledge calls for a principle of stability and necessity, identified by Plato with the Idea, Aristotle did not seek this principle in a separate entity but, truer to experience, found it in material reality itself, namely in substantial form. Corporeal things, then, are not just matter; they are matter and form. For all that, however, Aristotle did not repudiate the doctrine of separate substances - substances, that is, without any matter whatever.
Moreover, in his theory of knowledge Aristotle is at one with Plato on the insistence that to be intelligible the object must be abstracted (taken away, somehow) from matter. For him as for Plato, the intellect is a spiritual faculty; directly (as against indirectly) it can only know the "quiddity" of corporeal things; which is to say, the essence abstracted from matter. Consistent, also, with the spirit of Plato, and indeed implied in the principle of abstraction, is this other thought of Aristotle's, that an object is intelligible in proportion to its liberation from matter; the more immaterial it is, the more it is intelligible in itself - in itself, because not necessarily to every intellect. All of which St. Thomas will capsule in the assertion that the foundation, the essential condition, of intellection is immateriality. 18 As intimated, however, not all immateriality, which is to say not all abstraction from matter, is of the same degree. This brings us to the next heading, where, in particular, the immateriality proper to metaphysics should be noted.
2. The Three Degrees of Abstraction
Within the complex of speculative science Aristotle distinguishes three types or degrees of immateriality in the objects of knowledge and, correlatively, in the intellectual operations proportioned to the objects. These degrees correspond to the threefold classification of speculative science into physical, mathematical, and metaphysical, a classification traditionally accepted. Now, how does one degree differ from another? It differs according to the objective matter or material conditions left behind by the intellect in the abstractive process, or inversely, according to the matter and material conditions retained in the definitions which govern demonstration in a given science. The detailed analysis of this doctrine rests, however, with psychology or, perhaps more properly, with logic - major logic, that is, not infrequently identified with epistemology. We shall therefore content ourselves with a summarization.
On the level of physical science the intellect abstracts from matter so far as it is the principle of individuation, hence from individual or signate matter (materia signata); but matter is retained so far as it is the basis of sensible qualities. It is therefore called sensible or common matter (materia sensibilis vel communis). Since qualities, which are retained, are changeable or mobile, by that very fact is retained the changeability or mobility of things. In the second or mathematical degree, abstraction is made of the aforesaid common sensible matter, but kept under consideration is material substance as quantified, which in the Aristotelian tradition goes by the name "intelligible matter" (materia intelligibilis).19
In metaphysics, on the other hand, the abstraction is complete; abstracted, therefore, is all matter and motion of whatever kind. This degree of abstraction takes us into the realm of the utterly immaterial, which comprises both spiritual realities (God and the angels) and the primary concepts of being - being itself and the transcendentals, to mention the more obvious. The latter, that is, the primary concepts and the realities corresponding to them are independent or separate from matter in the sense that they need not be realized in corporeal things but are found as well in incorporeal or spiritual being.20
The special character of metaphysical abstraction will be pointed out at some length in the next chapter, when we analyze the notion of being. It is well, though, to anticipate a word of caution on the general subject of abstraction, and on metaphysical abstraction in particular. The intellect, we have said, attains in successive steps the three degrees of immateriality; but the activity by which it does this is not of a piece, or uniformly the same, as though the three steps were mere repetitions of the identical operation. The three acts of abstraction are not homogeneous, though comparable - analogous is really the word. To overlook this is to lapse into superficiality, not to say into gross misconception. True, the degrees of abstraction have in common that each is a removal of matter from consideration, but the manner of removal as well as the extent differs from one degree to the next. In the case of metaphysics St. Thomas prefers not even to call it abstraction but, more accurately, "separation," a term he does not apply to the first and second degree 21
The word "separation" must not, however, lead us astray in another direction. 'When, in other words, metaphysics is said to be the science of the "separate" or, if one prefers, of the "abstract," this does not imply that its object is divorced from real existence but only from the material conditions of existence. It could not be otherwise. Indeed, we shall see that the object of metaphysics is eminently real and concrete; so that far from being out of touch with reality, the metaphysician is in the full sense of the word more a realist than any of his fellows in the fraternity of scholars and scientists. And this is true whether he considers, under the aspect of being, the totality of things material and immaterial or whether, sectoring his horizon, he fixes attention on what is real above all because immaterial above all: pure spirits, that is, and infinitely above them, God.