Augustine, Confessions 10.3.24
“When I utter the word “forgetfulness” and I similarly see what I am naming, how would I acknowledge it if I have not remembered it? I don’t mean the word’s sound, but the thing that it means. If I had forgotten it, I would not be able to connect the meaning with the sound. So when I remember memory, then it is present in itself for itself at that moment. But when I recall forgetfulness, both memory and forgetfulness are there at the same time. Memory in allowing me to remember and forgetfulness is the thing I recall.
But what is forgetfulness if it isn’t the negation of memory? How can it be there in order to be remembered when I cannot remember it in its true presence? But if we retain what we have remembered in our memory, then if we did not remember forgetfulness, we would never be able to acknowledge that that word means when we hear it spoken. Forgetfulness is preserved by memory.”
16. (24) Quid, cum oblivionem nomino atque itidem agnosco quod nomino, unde agnoscerem nisi meminissem? non eundem sonum nominis dico, sed rem quam significat. quam si oblitus essem, quid ille valeret sonus agnoscere utique non valerem. ergo cum memoriam memini, per se ipsam sibi praesto est ipsa memoria. cum vero memini oblivionem, et memoria praesto est et oblivio, memoria qua meminerim, oblivio quam meminerim. Sed quid est oblivio nisi privatio memoriae? quomodo ergo adest ut eam meminerim, quando cum adest meminisse non possum? at si quod meminimus memoria retinemus, oblivionem autem nisi meminissemus, nequaquam possemus audito isto nomine rem quae illo significatur agnoscere, memoria retinetur oblivio.