Perhaps it would have done Descartes some good to read Gregory of Nyssa. Perhaps not. Regardless, for Gregory, there is great mystery in the human intellect. Man lacks the ability to fully comprehend himself, though surely he comprehends what is necessary for cognition, for piety, and for the other virtues. The incomprehensibleness of the human mind is a corollary of the imago Dei, not an affront to it. Since God is the archetype of the human mind, and since God is incomprehensible, then it follows that the image of that archetype would also be incomprehensible, yet in its own finite way.
In what way, then, is the human mind incomprehensible? In order to discern that, one must read Gregory himself On the Making of Man. In this, his expansion of Basil’s Hexameron, Gregory proceeds by way of negations to explain the nature of the mind. It is not confined to any member of the body, the heart, brain, etc. It is not divided by the various sense impressions that it receives from the body. That is, the mind is capable of experiencing one object, such as honey, by taste, by smell, and the other senses. The mind is simple. It is like the conductor of a grand symphony, bringing harmony to all of the bodily sensations by passing uniform judgments upon them. It is like the symphony itself. As the lungs exhale air and the muscles of the mouth move to create speech the body reflects the activities of a symphony composed of flute and lyre, playing in harmony with their conductor. The beauty of the mind and the grace of the body reflect the ultimate Beauty of God, the grand conductor. This beauty is beyond comprehension. It cannot be spoken or thought. It can only be experienced. In this experience of incomprehensibility, the incomprehensible God is known as in a reflection.
Gregory of Nyssa on the Nature of the Mind1
XI. That the nature of mind is invisible.
What then is, in its own nature, this mind that distributes itself into faculties of sensation, and duly receives, by means of each, the knowledge of things? That it is something else besides the senses, I suppose no reasonable man doubts; for if it were identical with sense, it would reduce the proper character of the operations carried on by sense to one, on the ground that it is itself simple, and that in what is simple no diversity is to be found. Now however, as all agree that touch is one thing and smell another, and as the rest of the senses are in like manner so situated with regard to each other as to exclude intercommunion or mixture, we must surely suppose, since the mind is duly present in each case, that it is something else besides the sensitive nature, so that no variation may attach to a thing intelligible.
“Who hath known the mind of the Lord?” the apostle asks; and I ask further, who has understood his own mind? Let those tell us who consider the nature of God to be within their comprehension, whether they understand themselves—if they know the nature of their own mind. “It is manifold and much compounded.” How then can that which is intelligible be composite? or what is the mode of mixture of things that differ in kind? Or, “It is simple, and incomposite.” How then is it dispersed into the manifold divisions of the senses? how is there diversity in unity? how is unity maintained in diversity?
But I find the solution of these difficulties by recourse to the very utterance of God; for He says, “Let us make man in our image, after our likeness.” The image is properly an image so long as it fails in none of those attributes which we perceive in the archetype; but where it falls from its resemblance to the prototype it ceases in that respect to be an image; therefore, since one of the attributes we contemplate in the Divine nature is incomprehensibility of essence, it is clearly necessary that in this point the image should be able to show its imitation of the archetype.
For if, while the archetype transcends comprehension, the nature of the image were comprehended, the contrary character of the attributes we behold in them would prove the defect of the image; but since the nature of our mind, which is the likeness of the Creator evades our knowledge, it has an accurate resemblance to the superior nature, figuring by its own unknowableness the incomprehensible Nature.