On The Holy Trinity by St. Augustine
Chapter 6.--How God is a Substance Both Simple and Manifold.
8. But if it is asked how that substance is both simple and manifold: consider, first, why the creature is manifold, but in no way really simple. And first, all that is body is composed certainly of parts; so that therein one part is greater, another less, and the whole is greater than any part whatever or how great soever. For the heaven and the earth are parts of the whole bulk of the world; and the earth alone, and the heaven alone, is composed of innumerable parts; and its third part is less than the remainder, and the half of it is less than the whole; and the whole body of the world, which is usually called by its two parts, viz. the heaven and the earth, is certainly greater than the heaven alone or the earth alone. And in each several body, size is one thing, color another, shape another; for the same color and the same shape may remain with diminished size; and the same shape and the same size may remain with the color changed; and the same shape not remaining, yet the thing may be just as great, and of the same color. And whatever other things are predicated together of body can be changed either all together, or the larger part of them without the rest. And hence the nature of body is conclusively proved to be manifold, and in no respect simple. The spiritual creature also, that is, the soul, is indeed the more simple of the two if compared with the body; but if we omit the comparison with the body, it is manifold, and itself also not simple. For it is on this account more simple than the body, because it is not diffused in bulk through extension of place, but in each body, it is both whole in the whole, and whole in each several part of it; and, therefore, when anything takes place in any small particle whatever of the body, such as the soul can feel, although it does not take place in the whole body, yet the whole soul feels it, since the whole soul is not unconscious of it. But, nevertheless, since in the soul also it is one thing to be skillful, another to be indolent, another to be intelligent, another to be of retentive memory; since cupidity is one thing, fear another, joy another, sadness another; and since things innumerable, and in innumerable ways, are to be found in the nature of the soul, some without others, and some more, some less; it is manifest that its nature is not simple, but manifold. For nothing simple is changeable, but every creature is changeable.