On the Immortality of the Soul

...then, that every soul is separated, even the irrational and natural, or vegetative; in which matter he condemns Numenius as if he were deceived by certain Platonic words. On the other hand, he says that Alexander thought every soul to be inseparable and tried to distort Aristotle’s meanings so that they might seem to support his own view. He contends that this was not possible because, among the diverse opinions concerning separation, Aristotle walked such a middle path that he showed one soul to be separable and another inseparable, especially in his very work On the Parts of Animals; and he asserted that each part is marked and distinguished by a certain manifest vital operation. He inquired whether it was necessary to name this operation "soul," or a "part of the soul," or "not without the soul," as one who knew the great breadth, or rather the depth, of souls.

Likewise, when he asked whether discussing every soul pertained to the natural philosopher, or not every soul but only that which is not without matter, he thereby indicated that some part was separable. For if, he says, the natural philosopher discusses every soul, he will also discuss the intellect; and if the intellect, then certainly intelligible things, for just as the sense is of sensible things, so the intellect is of intelligible things. But to discuss intelligible things pertains to the First Philosopher. And again, in that work, when speaking of the affections of the soul—anger, desire, and the rest—since they are inseparable from the body, he says that for this reason it pertains to the natural philosopher to contemplate the soul which is not without matter; from which it follows that he clearly saw that the soul is sometimes disjoined and plainly separated from matter.

In the first book of On the Soul as well, he asserted that the intellect seems to be a certain essence which would not be corrupted, since that would chiefly happen through the obscurity of old age. In the second book, however, he inquires whether the powers of that soul are the soul itself, or rather its parts. Concerning the intellect and the contemplative power, he says it is not yet manifest; and it seems to be another kind of soul, and to this alone it belongs to be separated, as the perpetual from the corruptible. But in the third book, he judges that the intellect by which the soul understands and is prudent is not mixed with the body. Again, when he treats of the difference between the intellect and the sense, he teaches that the sense, having been affected by a more vehement sensible object, is weakened, so much so that it does not perceive lesser sensible objects. But the intellect, through which it perceives greater things, is rendered more fit for perceiving more sublime things; and the cause