Historically, both the practice and theory of harmony are of comparatively recent devel ment. The simple chords which make up the bulk of ordinary modern music were preceded by something far more complicated. After be ing confined from time immemorial to the pro gression of a single voice, music, from the 9th century on, began to spread out into the simul taneous movement of several parts, the result finally being the complicated tissue of _poly phonic music which we meet with in the Neth erlands and Italy previous to the 17th century. Not until this time do the chance harmonies of simultaneously progressing voices become con solidated into single, block-like chords. The first premeditated use of chords in the modern sense seems to have been made by the founders of opera, who lived about the year 1600, and especially by Monteverde, who stands out as one of the most gifted of this enthusiastic group of men. Theoretically the rules of harmony were first laid down by Rameau in his de l'Harmonie,* published in the year 1722. It was Rameau who deduced the chords which were the object of his research from the over tones of their root-notes. Tartini, on the other hand, invoked the so-called ((combinational" tones for the elaboration of his theories. Not
until the time of Helmholtz was the true sig nificance of these discoveries brought to light and given a scientific foundation. Like all other branches of knowledge, harmony has been un dergoing changes with the lapse of time and transformation of musical taste. No art is subject to such variations as music in what is considered novel and beautiful. Hence its the ory, likewise, has been subject to corresponding fluctuations. To give but a single example, the parallel progression of fifths and octaves, which in the earliest days of harmonic devel opment was the rule, was later forbidden as a deadly offense against the canons of good taste, and remained so for many centuries. Of late, however, this rule has lost much of its rigor, and parallel fifths and octaves are now used again with comparative freedom. Here, as in other arts, the genius of great creative minds has fashioned new modes of expression, and traditional formulas have been powerless to re sist. Hence harmony is a fluid branch of the ory; and while some of its rules, based on scientific laws of sound, may remain constant, others will be transformed so as to agree with the varying practice of great musicians.