“ Historically, however, the sense has developed from its stricter musical meaning of a scale (the recognized musical scale of any period) , originating in the medieval “great scale,” of which the invention has usually been ascribed to Guido of Arezzo (q.v.) in the 11th century. ”

“ To this scale of four notes, G, A, ͡♭ B, C, were subsequently added a note below and a note above, which made the hexachord with the semitone between the 3rd and 4th both up and down, as F, G, A, ͡♭ B, C, D. It was at a much later date that the 7th, our leading note, was admitted into a key, and for this the first two letters of the last line of the above-named hymn, “Sanctus Johannes,” would have been used, save for the notion that as the note Mi was at a semitone below Fa, the same vowel should be heard at a semitone below the upper Ut, and the syllable Si was substituted for Sa. ”