Of the word ΕΙ engraven over the gate of Apollo's temple at Delphi (8)

I answered therefore that Eustrophus has excellently solved the difficulty by number. For (said I) since all number is distributed into even and odd, unity is in efficacy common to them both,—for that being added to an even number, it makes it odd, and to an odd, it makes it even, two constituting the beginning of the even, and three of the odd. Now the number of five, composed of these two, is deservedly honored, as being the first compound made of the first simple numbers, and is called the marriage, for the resemblance of the odd with the male, and the even with the female. For in the divisions of the numbers into equal parts, the even, being wholly separated, leaves a certain capacious beginning and space in itself; but in the odd, suffering the same thing, there always remains a middle, of generative distribution, by which it is more fruitful than the other, and being mixed is always master, never mastered. For by the mixture of both, even and odd together, there is never produced an even number but always an odd. But which is more, either of them added to and compounded with itself shows the difference; for no even joined with another even ever produced an odd, or went forth of its proper nature, being through weakness unable to generate another and imperfect. But odd numbers mixed with odd do, through their being every way fruitful, produce many even ones. Time does not now permit us to set down the other powers and differences of numbers. Therefore have the Pythagoreans, through a certain resemblance, said that five is the marriage of the first male and the first female number. This

also is it for which it is called Nature, by the multiplication of itself determining again into itself. For as Nature, taking a grain of wheat for seed and diffusing it, produces many forms and species between, by which she brings her work to an end, but at last she shows again a grain of wheat, restoring the beginning in the end of all; so, while the rest of the numbers, when they are multiplied into others, terminate by the increase only those of five and six, multiplied by themselves, bring back and preserve themselves. For six times six makes thirty-six, and five times five makes twenty-five. And again, six does this once, and only after one manner, to wit, when it is squared. But this indeed befalls five both by multiplication and by composition with itself, to which being added, it alternatively makes itself and ten; and this as far as all number can extend, this number imitating the beginning or first Cause which governs the universe. For as that first Cause, preserving the world by itself, does reciprocally perfect itself by the world, as Heraclitus says of fire,

Fire turns to all things, and all things to fire;

and as money is changed for gold, and gold for money; so the congress of five with itself is framed by Nature to produce nothing imperfect or strange, but has limited changes; for it either generates itself or ten, that is, either what is proper to itself, or what is perfect.