Commentary on the First Book of Euclid's Elements

It is necessary that mathematical substance should be considered as holding a middle place, neither among the first of existing things nor among the last and simply divided things, but as occupying a middle region between the indivisible, simple, uncompounded, and impartible hypostases fundamental realities, and those which are divisible and defined by all kinds of manifold divisions. For that which is always uniform, permanent, and irrefutable shows itself to be superior to the forms carried in matter, while the discursive nature of the epibolai intellectual projections/acts of apprehension—which makes use of the dimensions of underlying subjects and constructs some things from others—gives it a lower rank than that of the indivisible nature which is perfectly established within itself. For this reason, I think, Plato divided the knowledge of existing things according to the primary, middle, and final hypostases, and attributed to the indivisible things the intelligible knowledge, which divides the intelligible things all at once and with simplicity, and which surpasses all other forms of knowledge by its immateriality, purity, and unified approach and contact with existing things. To those things which are divisible and possess the lowest nature, and to all sensible things, he attributed opinion, which apprehends truth dimly. To the middle things, such as are the species of mathematics, he attributed dianoia discursive reasoning, which falls short of the indivisible nature but is set above the divisible.

Proclus Diadochus on the first book of Euclid's Elements. Book I.