And nevertheless, even though the unity of the concrete spiritual substance and its faculties be so far higher than a mechanical or even an organic unity, it is not perfect. Even though the faculties of the soul be determinations of its substance, even though they flow from it as actualities demanded by its essence for the normal and natural development of its being, still it is a complete subsisting essence of its kind without them; it possesses its _essential_ perfection without them, so that however intimate be their union with it they can never form one essence with it; it needs them only for the fuller development of its being by acquiring further _intermediate_ perfections and thus attaining to its _final_ perfection (46). And here we touch on the most fundamental ground of the distinction, in all created things, between their substance and their accidental perfections. Unlike the Necessary, Absolute Being, whose infinite perfection is the eternal actuality of His essence, no creature possesses the actuality of its being _tota simul_, but only by a progressive development whereby it gradually acquires really new intermediate and final perfections, really distinct from, though naturally due to, its essence. Hence, even though some of its accidents—properties such as the powers and faculties we have been discussing—be not really distinct from the essence wherewith they are necessarily connected, this is not true of its acquired habits and dispositions, or of the activities which proceed from these latter as their proximate principles. At the same time the concrete being is, at every moment of its existence and development, a real unity, but a unity which, involving in itself as it does a real multiplicity of distinct principles, must ever fall infinitely short of the perfect type of real unity—that realized only in the Self-Existent, Necessary Being. CHAPTER IX. NATURE AND PERSON. 70. SOME DIVISIONS OF SUBSTANCES.—In the preceding chapter we discussed the nature of substance and accident in general, and the relation between a substance and its accidents. We must next examine the category of substance more in detail, terminating as it does in the important concept of personality or person. This latter conception is one which must have its origin for all philosophers in the study of the human individual, but which, for scholastic philosophers, is completed and perfected by the light of Christian Revelation. We shall endeavour to show in the first place what can be gathered from the light of reason about the constitution of personality, and also briefly to note how Christian Revelation has increased our insight into the perfections involved in it. As leading up to the concept of person, we must set forth certain divisions or classifications of substance: into _first_ and _second_ substances, and into _complete_ and _incomplete_ substances.(277)