Procli Diadochi In Primum Euclidis Elementorum Librum Commentarii

...if we collect the logoi of mathematics from sensible things, why is it not necessary to say that the proofs which consist of sensible things are better than those from the always more holistic and simpler eide forms? For we say that the causes are everywhere appropriate to the proofs for the hunt of the sought-after truth. If, then, particular things are the causes of universal ones, and sensible things are the causes of dianoēta discursive objects, what mechanism makes it so that the definition of proof refers more to the universals instead of the divisible and the dianoēta, and declares the essence [to be] more akin to the proofs prior to the sensible things? For even if someone were to prove that the isosceles triangle has angles equal to two right angles, and understands the equilateral and the scalene in a similar way, it is the one who has proven it for every triangle, and simply, who possesses the knowledge as such. And again, that the universal is better than the particular for the purpose of proof, and subsequently that proofs are from universals, and that the things from which proofs arise are prior and preceding in nature to the individuals and are the causes of the things being demonstrated. Therefore, the demonstrative sciences are far from observing the things that are secondary and dimmer, such as sensible things, but instead they contemplate the things graspable by dianoia discursive thought, which are more perfect than the things known by sense-perception and opinion.

Furthermore, we say thirdly that those who state these things also make the soul more dishonorable than matter. For if matter receives the essential, more existent, and clearer things from nature, while the soul [is] second...