28 And yet, that we may not be as ignorant when we leave you as before, let us hear from you how you say that the soul, on being enwrapt in an earthly body, has no recollection of the past; while, after being actually placed in the body itself, and rendered almost senseless by union with it, it holds tenaciously and faithfully the things which many years before, eighty if you choose to say so, or even more, it either did, or suffered, or said, or heard. For if, through being hampered by the body, it does not remember those things which it knew long ago, and before it came into this world, there is more reason that it should forget those things which it has done from time to time since being shut up in the body, than those which it did before entering it, while not yet connected with men.
For the same body which deprives of memory the soul which enters it, should cause what is done within itself also to be wholly forgotten; for one cause cannot bring about two results, and these opposed to each other, so as to make some things to be forgotten, and allow others to be remembered by him who did them. But if souls, as you call them, are prevented and hindered by their fleshly members from recalling their former knowledge, how do they remember what has been arranged in these very bodies, and know that they are spirits, and have no bodily substance, being exalted by their condition as immortal beings? how do they know what rank they hold in the universe, in what order they have been set apart from other beings?
How they have come to these, the lowest parts of the universe? What properties they acquired, and from what circles, in gliding along towards these regions? How, I say, do they know that they were very learned, and have lost their knowledge by the hindrance which their bodies afford them? For of this very thing also they should have been ignorant, whether their union with the body had brought any stain upon them; for to know what you were, and what today you are not, is no sign that you have lost your memory, but a proof and evidence that it is quite sound.
Source: Against the Heathen (New Advent)