FIRST PART OF THE PROLOGUE.

It is necessary that mathematical substance occupies a middle position, neither among the first of those things that are, nor among the last, removed from simple division, but rather it must take up the middle ground between the indivisible, simple, 5 uncompounded, and undivided substances, and those that are divisible and bounded by all kinds of complex and various divisions. For that which is always unchanging, permanent, and irrefutable—the accounts concerning it—shows that it excels over the forms borne in matter; but the discursive that which proceeds step-by-step nature of its apprehensions, and that which makes use of the dimensions of the underlying subjects, and that which prepares some things from other principles, gives it a rank inferior to the indivisible nature which is perfectly established within itself. For this reason, I think, Plato also divided the knowledge of beings by the first, middle, and last substances, and he attributed to the indivisible the intelligible, which is known all at once and with...

Proclus Diadochus on the first book of Euclid’s Elements.