Procli Diadochi In Primum Euclidis Elementorum Librum Commentarii

...simplicity, dividing the intelligible things and surpassing all other forms of knowledge by immateriality, purity, and a unified approach and contact with beings, while to the divisible things, which have attained the lowest nature, and to all sensible things, he attributed opinion, which apprehends the truth only dimly. And to the middle things, such as the forms of mathematics, which both fall short of the indivisible nature and are placed above the divisible, he attributed discursive thought. For this is second to intellect and the highest science, but it is more perfect, more accurate, and purer than opinion. For it proceeds and unfolds the measurelessness of the intellect and unrolls that which is coiled up in intellectual apprehension, but then it gathers the divided things again and carries them back to the intellect. Therefore, just as forms of knowledge are separated from one another, so too the things known are distinguished by nature. Intelligible things are spread over all by unified existences, while sensible things are left behind by all primary substances. Mathematical things, and generally discursive things, have obtained a middle rank, abounding in the former by division, while excelling the latter in immateriality; and while falling short of the former in simplicity, they exist before the latter in accuracy. They have clearer reflections of the intelligible substance than sensible things, yet they are nonetheless images, and they grasp the indivisible things in a divisible manner.

A schematic bracket diagram in the apparatus classifies the types of knowledge. The terms primary and last are bracketed together, converging toward the term middle on the right.