[14] The power of this number reaches also to the most beneficent of the arts: in grammar, for instance, the best and most effective of the letters, namely the vowels, are seven in number: in music we may fairly call the seven-stringed lyre the best of instruments, because the enharmonic genus, which as we know is the most dignified of those used in melodies, is best brought out when that instrument renders it. Sevenfold are the modulations in pronunciation—acute, grave, circumflex, aspirated and unaspirated, long, short.
[15] Further, seven is the first number after the perfect number six, and the same in some sort with the number one. Whereas other numbers within the decade are either produced by or produce those within the decade and the decade itself, the number seven neither produces any of the numbers within the decade nor is produced by any. By reason of this the Pythagoreans, indulging in myth, liken seven to the motherless and ever-virgin Maiden, because neither was she born of the womb nor shall she ever bear.