The only form of music used in the Church, up to the beginning of the twelfth century, the only form of music ever given its official sanction, was the Gregorian chant or plain song, which consists in a single unaccompanied series of tones set to the liturgic text, intoned by priest or choristers, and for many centuries used exclusively throughout the entire service. It has not only no harmony, but, properly speaking, no meter or rhythm, being dependent for time-measurement on the prose text it accompanies. “It follows” says Mr. Dickinson,[9] “the phrasing, the emphasis, and the natural inflections of the voice in reciting the text, at the same time that it idealizes them. It is a sort of heightened form of speech, a musical declamation, having for its object the intensifying of the emotional powers of ordinary spoken language. It stands to true song or tune in much the same relation as prose to verse, less impassioned, more reflective, yet capable of moving the heart like eloquence.” Having neither harmonic nor metrical relationship, it had, of course, no proper structure of its own; and so long as it was used in this primary way, sung in unison or even in two parts at the interval of an octave, there was little about it that could properly be called musical at all. But after a while it occurred to some one to let a second set of voices sing the same chant at an interval of a fifth above the first.[10] This scheme, which, simple as it was, contained the seeds of wonderful developments, was probably first recommended by several practical advantages. When the chant was sung by two choirs, one made up of the high voices (soprano and tenors) and the other of the low voices (contraltos and basses) the interval of the octave was practically inconvenient because the low voices could not use their highest tones without throwing the high voices out of range, and the high voices could not use their lowest tones without similarly embarrassing the low ones. When the interval of the fifth was used, on the contrary, practically all the tones in both ranges, which are by nature about a fifth apart,[11] became available. This was a very practical argument in favor of chanting “at the fifth.” An even stronger one was the fact that, while fifths, like octaves, are harmonious and pleasant to the ear, without harshness or discordance, they are richer than octaves, and their constituents stand out distinct instead of merging into one impression, as do tones an octave apart; so that the practice of Organum, or chanting at the fifth, was harmonically sweet and full as well as melodically interesting. Organum came therefore into general and wide use in the mediæval church. Hucbald, a monkish writer of the tenth century, gives the following example of a fragment of plain chant “organized,” or sung by two voices a fifth apart: [Music: score] [Illustration: FIGURE II. EXAMPLE OF ORGANUM.]