On the Principles of Arithmetic and On the Principles of Music

...is led toward the more certain things of understanding. For there are certain steps and fixed measures of progression by which one can ascend and advance, so that these disciplines may again illuminate that eye of the mind—which, as Plato says In The Republic (527d-e), Plato argues that the study of mathematics purifies the "eye of the soul," which is more valuable than ten thousand physical eyes., is more worthy of being saved and established than many physical eyes, because truth can be investigated or perceived by that light alone—this eye, I say, which has been submerged and blinded
5 by the bodily senses.
┌ Which, therefore, among these must be learned first, if not that which holds the position of a principle and, in a way, the role of a mother to the rest?
10 This is arithmetic. For this is prior to all others, not only because God, the creator of this massive world, held this as the first exemplar of his own reasoning and established all things according to it—whatever things found harmony in their assigned order through numbers by the work of reason—but arithmetic is also declared prior for this reason:
15 that whatever things are prior by nature, if these are removed, the posterior things are taken away at the same time; but if the posterior things perish, nothing of the state of the prior substance is changed. For example, "living creature" original: "animal" is prior to "human." For if you take away "living creature,"
20 the nature of "human" is immediately destroyed; but if you remove "human," the "living creature" will not perish. And conversely, those things are always posterior which bring something else along with them; those are prior which, when spoken of, draw nothing of the posterior with them, as is the case with this same human. For if you say "human,"
25 you simultaneously name "living creature," for a human is the same thing as a living creature; but if you say "living creature," you have not simultaneously introduced the species of "human," for a living creature is not the same thing as a human. This same principle seems to apply to geometry and arithmetic. For if
30 you take away numbers, from where will come the triangle, or the square, or whatever is dealt with in geometry? All of these [are derived from] the [descriptions] of numbers...