5. Again, there is movement: all bodily movement is uniform; failing an incorporeal soul, how account for diversity of movement? Predilections, reasons, they will say; that is all very well, but these already contain that variety and therefore cannot belong to body which is one and simplex, and, besides, is not participant in reason- that is, not in the sense here meant, but only as it is influenced by some principle which confers upon it the qualities of, for instance, being warm or cold.
Then there is growth under a time-law, and within a definite limit: how can this belong strictly to body? Body can indeed be brought to growth, but does not itself grow except in the sense that in the material mass a capacity for growing is included as an accessory to some principle whose action upon the body causes growth.
Supposing the soul to be at once a body and the cause of growth, then, if it is to keep pace with the substance it augments, it too must grow; that means it must add to itself a similar bodily material. For the added material must be either soul or soulless body: if soul, whence and how does it enter, and by what process is it adjoined [to the soul which by hypothesis is body]; if soulless, how does such an addition become soul, falling into accord with its precedent, making one thing with it, sharing the stored impressions and notions of that initial soul instead, rather, of remaining an alien ignoring all the knowledge laid up before?
Would not such a soulless addition be subject to just such loss and gain of substance, in fact to the non-identity, which marks the rest of our material mass?
And, if this were so, how explain our memories or our recognition of familiar things when we have no stably identical soul?
Assume soul to be a body: now in the nature of body, characteristically divisible, no one of the parts can be identical with the entire being; soul, then, is a thing of defined size, and if curtailed must cease to be what it is; in the nature of a quantitative entity this must be so, for, if a thing of magnitude on diminution retains its identity in virtue of its quality, this is only saying that bodily and quantitatively it is different even if its identity consists in a quality quite independent of quantity.
What answer can be made by those declaring soul to be corporeal? Is every part of the soul, in any one body, soul entire, soul perfectly true to its essential being? and may the same be said of every part of the part? If so, the magnitude makes no contribution to the soul's essential nature, as it must if soul [as corporeal] were a definite magnitude: it is, as body cannot be, an "all-everywhere," a complete identity present at each and every point, the part all that the whole is.
To deny that every part is soul is to make soul a compound from soulless elements. Further, if a definite magnitude, the double limit of larger or smaller, is to be imposed upon each separate soul, then anything outside those limits is no soul.
Now, a single coition and a single sperm suffice to a twin birth or in the animal order to a litter; there is a splitting and diverging of the seed, every diverging part being obviously a whole: surely no honest mind can fail to gather that a thing in which part is identical with whole has a nature which transcends quantity, and must of necessity be without quantity: only so could it remain identical when quantity is filched from it, only by being indifferent to amount or extension, by being in essence something apart. Thus the Soul and the Reason-Principles are without quantity.
