Since harmony was unknown during the first one thousand years or more of the Christian era, and instrumental music had no independent existence, the whole vast system of chant melodies was purely unison and unaccompanied, its rhythm usually subordinated to that of the text. Melody, unsupported by harmony, soon runs its course, and if no new principle had been added to this antique melodic method, European music would have become petrified or else have gone on copying itself indefinitely. But about the eleventh century a new conception made its appearance, in which lay the assurance of the whole magnificent art of modern music. This new principle was that of harmony, the combination of two or more simultaneous and mutually dependent parts. The importance of this discovery needs no emphasis. It not only introduced an artistic agency that is practically unlimited in scope and variety, but it made music for the first time a free art, with its laws of rhythm and structure no longer identical with those of language, but drawn from the powers that lie inherent in its own nature. Out of the impulse to combine two or more parts together in complete freedom from the constraints of verbal accent and prosody sprang the second great school of church music, which, likewise independent of instrumental accompaniment, developed along purely vocal lines, and issued in the contrapuntal chorus music which attained its maturity in the last half of the sixteenth century. This mediaeval school of _a capella_ polyphonic music is in many respects more attractive to the student of ecclesiastical art than even the far more elaborate and brilliant style which prevails to-day. Modern church music, by virtue of its variety, splendor, and dramatic pathos, seems to be tinged with the hues of earthliness which belie the strictest conception of ecclesiastical art. It partakes of the doubt and turmoil of a skeptical and rebellious age, it is the music of impassioned longing in which are mingled echoes of worldly allurements, it is not the chastened tone of pious assurance and self-abnegation. The choral song developed in the ages of faith is pervaded by the accents of that calm ecstasy of trust and celestial anticipation which give to mediaeval art that exquisite charm of naïveté and sincerity never again to be realized through the same medium, because it is the unconscious expression of an unquestioning simplicity of conviction which seems to have passed away forever from the higher manifestations of the human creative intellect.