That the thing perceived, I replied, is not the same as the thing not perceived, I grant; but I do not discover any answer to our question in such a statement; it is not yet clear to me what we are to think that thing not-perceived to be; all I have been shown by your argument is that it is not anything material; and I do not yet know the fitting name for it. I wanted especially to know what it is, not what it is not.
We do learn, she replied, much about many things by this very same method, inasmuch as, in the very act of saying a thing is not so and so, we by implication interpret the very nature of the thing in question. For instance, when we say a guileless, we indicate a good man; when we say unmanly, we have expressed that a man is a coward; and it is possible to suggest a great many things in like fashion, wherein we either convey the idea of goodness by the negation of badness , or vice versâ. Well, then, if one thinks so with regard to the matter now before us, one will not fail to gain a proper conception of it. The question is—What are we to think of Mind in its very essence? Now granted that the inquirer has had his doubts set at rest as to the existence of the thing in question, owing to the activities which it displays to us, and only wants to know what it is, he will have adequately discovered it by being told that it is not that which our senses perceive, neither a colour, nor a form, nor a hardness, nor a weight, nor a quantity, nor a cubic dimension, nor a point, nor anything else perceptible in matter; supposing, that is, that there does exist a something beyond all these.
St. Gregory of Nyssa and St. Macrina the Younger in Gregory of Nyssa's On the Soul and the Resurrection.