The Greek modes were revised by Claudius Ptolemy, and on the basis of his revisions was established the system of the mediæval church. In it the claims of the medium began to receive further attention, and the next step was the gradual elaboration of counterpoint, that is, the combination of simultaneous voice parts, each independent, but all conducing to a result of uniform and coherent texture. Starting from the crude origins of descant and faux-bourdon, the new method steadily grew and developed, through Dunstable, Dufay, Josquin, and a host of other great writers, until it reached the second universal landmark in the magnificent climax of Palestrina. If the ecclesiastical modes had been final, music would never have advanced beyond the 'Missa Papæ Marcelli,' and the 'Æterna Christi Munera.'
But the modes were not final. For certain scientific reasons, into which it is here needless to enter, they were incapable either of a common tonality or of a coherent system of modulation. Hence, while the organisation of harmony could be carried by the ecclesiastical composers to a high degree of perfection, the organisation of key lay outside their horizon altogether. And while they were busy, like the schoolmen, in 'applying a method received on authority to a matter received on authority,' the unrecognised popular musicians, who had never heard of Ptolemy, and cared nothing about counterpoint, were writing tunes in which our modern scale-system begins to make a tentative and hesitating appearance. It is not too much to say that the dances collected in Arbeau's Orchesographie come nearer to our sense of tonality than all the masses and madrigals that contemporary learning could produce. In a word, the growth of harmony belongs to the Church, the growth of key to the people.
Then came the most important dynamic change in all musical history: the Florentine revolution of 1600. Its ostensible object was frankly dramatic--the revival of Greek tragedy under such altered conditions as were implied by the change of language and civilisation: its real importance was that it destroyed the convention of the modes, and called tonality from the country fair to the theatre and the concert-room. For a while, no doubt, the dramatic ideal overpowered everything else, and even the Church left off writing masses and took to oratorios instead; but when pure music reasserted itself, it found an entirely new set of problems waiting for solution. Harmony had to be organised, not on the basis of the mode, but on the basis of the modern scale, and thus had to take into account a question of key-relationship which had never fallen within the scope of the ecclesiastical period. And hence followed a line of development beginning about the time of the younger Gabrieli, and passing through the great choral composers of the seventeenth and eighteenth centuries until the third landmark of our musical history was attained in the person of John Sebastian Bach. His polyphony, as applied to the emotional expression of his time, is simply the best of which the art of music is capable. Given the phrases which he employed as subjects, the human mind cannot conceive their being treated with a more complete harmonic perfection.