Time to get schooled, so pack a lunch:
"THERE are two factors. First is the background. This concerns the universal 'stability' of the so-called 'perfect fifth'. When you blow a pipe of any sort, blowing harder gives you higher notes. To start with, you get an octave, then a perfect fifth, then another octave. A series of four different pitches, three of which are really the same note, and one, the 'perfect fifth' different. But sounding very tranquil and stable, and used everywhere in the world. It gave two intervals, the perfect fifth (from the octave up to the fifth) and the perfect fourth (from the Fifth up to the next octave). Around the ninth century there developed the first form of 'harmony' in the west, which consisted of a tune note, with the 'harmony' note a parallel fourth or a fifth. Second there is the context. In the days when the 'octave' really did repeat on the eighth note (as opposed to now, when it repeats on the thirteenth!), the only way you could get a different scale was to start on a different note. The scales, or 'modes', each had their own sound and feel, and melodies such as those in Gregorian Chant were made up of notes from just one of them. They all worked except for the scale you get if you play from B to B. This so-called Locrian mode was the only one where the fifth note was not a perfect fifth. It went against everything music appeared to stand for, and was christened 'diabolus in musica' the devil in music, and never used. But there is an interesting footnote to this. The problem led to adjustments at both ends of the B to F devilish interval. Composers either flattened the B until it was a perfect fifth below F, giving us the new note 'B flat', or they sharpened the F until it was a perfect fifth above the B, giving us the new note 'F sharp'. Among other things, this meant that a G major scale could now be played (using F sharp instead of F) and so could an F major scale (using B flat instead of B). And that's how harmony began, folks."
--Conrad Cork, Leicester (author of "The New Guide to Harmony with Lego Bricks").
"THERE are two factors. First is the background. This concerns the universal 'stability' of the so-called 'perfect fifth'. When you blow a pipe of any sort, blowing harder gives you higher notes. To start with, you get an octave, then a perfect fifth, then another octave. A series of four different pitches, three of which are really the same note, and one, the 'perfect fifth' different. But sounding very tranquil and stable, and used everywhere in the world. It gave two intervals, the perfect fifth (from the octave up to the fifth) and the perfect fourth (from the Fifth up to the next octave). Around the ninth century there developed the first form of 'harmony' in the west, which consisted of a tune note, with the 'harmony' note a parallel fourth or a fifth. Second there is the context. In the days when the 'octave' really did repeat on the eighth note (as opposed to now, when it repeats on the thirteenth!), the only way you could get a different scale was to start on a different note. The scales, or 'modes', each had their own sound and feel, and melodies such as those in Gregorian Chant were made up of notes from just one of them. They all worked except for the scale you get if you play from B to B. This so-called Locrian mode was the only one where the fifth note was not a perfect fifth. It went against everything music appeared to stand for, and was christened 'diabolus in musica' the devil in music, and never used. But there is an interesting footnote to this. The problem led to adjustments at both ends of the B to F devilish interval. Composers either flattened the B until it was a perfect fifth below F, giving us the new note 'B flat', or they sharpened the F until it was a perfect fifth above the B, giving us the new note 'F sharp'. Among other things, this meant that a G major scale could now be played (using F sharp instead of F) and so could an F major scale (using B flat instead of B). And that's how harmony began, folks."
--Conrad Cork, Leicester (author of "The New Guide to Harmony with Lego Bricks").
