§3 Augustine, we might say, does describe a system of communication, only not everything that we call language is this system. And one has to say this in many cases where the question arises "Is this an appropriate description or not?" The answer is: "Yes, it is appropriate, but only for this narrowly circumscribed region, not for the whole of what you were claiming to describe."
It is as if someone were to say: "A game consists in moving objects about on a surface according to certain rules..."--- and we replied: You seem to be thinking of board games, but there are others. You can make your definition correct by expressly restricting it to those games.