[97] 7 (or “7th”) exhibits yet another beauty belonging to it, a most sacred object for our mind to ponder. Being made up as it is of 3 and 4 it is a presentation of all that is naturally steadfast and upright in the universe. How it is this, we must point out. The right-angled triangle, the starting-point of figures of a definite shape, is made up of certain numbers, namely 3 and 4 and 5:3 and 4, the constituent parts of 7, produce the right angle: for the obtuse and acute angle are manifestations of irregularity and disorder and inequality: for one such angle can be more obtuse or more acute than another: whereas one right angle does not admit of comparison with another, nor can it be more “right” than another, but remains as it is, never changing its proper nature. Now if the right-angled triangle is the starting-point of figures of a definite kind, and the essential factor in this triangle, namely the right angle, is supplied by the numbers which constitute 7, namely 3 and 4 together, 7 would reasonably be regarded as the fountain-head of every figure and every definite shape.
[98] In addition to what we have already said we are bound to mention this further point, namely that 3 is the number belonging to a superficies—for a point falls under the head of 1, a line under that of 2, and a superficies of 3—while 4 belongs to a solid, by means of the addition of 1, depth being added to superficies. From this it is manifest that 7 is so constituted as to be the starting-point of all plane and solid geometry, or (to put it concisely) alike of things corporeal and incorporeal.