XLII. (126) And the power of this number does not exist only in the instances already mentioned, but it also pervades the most excellent of the sciences, the knowledge of grammar and music. For the lyre with seven strings, bearing a proportion to the assemblage of the seven planets, perfects its admirable harmonies, being almost the chief of all instruments which are conversant about music. And of the elements of grammar, those which are properly called vowels are, correctly speaking, seven in number, since they can be sounded by themselves, and when they are combined with other letters, they make complete sounds; for they fill up the deficiency existing in semi-vowels, making the sounds whole; and they change and alter the natures of the mutes inspiring them with their own power, in order that what has no sound may become endowed with sound. (127) On which account it appears to me that they also originally gave letters their names, and acting as became wise men, did give the name to the number seven from the Respect[the word used is sebasmos, as if hebdomas were derived from that; and the Romans formed septem from hepta, by the addition of s.] they had for it, and from regard to the dignity inherent in it. But the Romans, adding the letter S, which had been omitted by the Greeks, show still more conspicuously the correct etymological meaning of the word, calling it septem, as derived from semnos, venerable, as has been said before, and from sebasmos, veneration.