22. May we think that the mode of the soul's presence to body is that of the presence of light to the air?
This certainly is presence with distinction: the light penetrates through and through, but nowhere coalesces; the light is the stable thing, the air flows in and out; when the air passes beyond the lit area it is dark; under the light it is lit: we have a true parallel to what we have been saying of body and soul, for the air is in the light quite as much as the light in the air.
Plato therefore is wise when, in treating of the All, he puts the body in its soul, and not its soul in the body, and says that, while there is a region of that soul which contains body, there is another region to which body does not enter- certain powers, that is, with which body has no concern. And what is true of the All-Soul is true of the others.
There are, therefore, certain soul-powers whose presence to body must be denied.
The phases present are those which the nature of body demands: they are present without being resident- either in any parts of the body or in the body as a whole.
For the purposes of sensation the sensitive phase of the soul is present to the entire sensitive being: for the purposes of act, differentiation begins; every soul phase operates at a point peculiar to itself.