FOR thousands of years men sang in unison, or men and women (or men and boys) sang in octaves, as the different pitch of their voices dictate-which is nearly the same thing as singing in unison.
Then from the singing in parallel octaves was added (Early Organum, about 900-1050) the practice of singing in parallel 5ths and 4ths--all these intervals being of that open, hollow, bare-sounding character which is technically described by the word 'perfect.'
Before long it became evident that an agreeable variety could be obtained by the interspersing amongst these 'perfect' intervals of 'imperfect' ones, say of 3rds and 6ths amongst the 4ths and 5ths and 8ves. This was a broad step forward, for it involved a new conception.
No longer was any voice which accompanied the main theme, or plainsong, compelled to move slavishly with it in parallel, so merely coloring it by the unvaried pigment of a fixed interval; this accompanying part now expressed something of its own individuality, and if there were several such accompanying parts just as many individualities could express themselves. But at the stage we are at present discussing a good deal of parallelism remained, and the development of individuality of parts had not progressed very far.
However, it is evident that nothing but work and time now stood between composers and the perfection of choral style just described and demonstrated, and work and time (another four to four-and-a-half centuries of them) duly brought about this perfection.