plain-song moved naturally in metrical rhythm, and in which the descant accompanied it note for note. In the _conductus_ composers made use of all the devices of imitation and sequence which were at their command. Finally, the third class of compositions named above is represented by the Motet. The Motet is by far the most remarkable of all forms invented by the mensuralists. In the first place, a melody, usually some bit of plain-song, was written down in a definite rhythmical formula. There were several of these formulæ, called _ordines_, at the service of the composers. The tenor part was made up of the repetition of this short formal phrase. Over this two descanting parts were set, which might be original with the composer, but which later were almost invariably two songs, preferably secular songs. These two songs were simply forced into rhythmical conformity to the tenor. They were slightly modified so as to come into consonance with each other and with the tenor at the beginning and end of the lines. Apart from this they were in no way related, either to each other or to the tenor. So came about the remarkable series of compositions in which three distinct songs, never intended to go together, are bound fast to each other by the rules of measured music, in which the tenor drones a nonsense syllable, while the descant and the treble may be singing, the one the praises of the Virgin, the other the praises of good wine in Paris. This is surely the triumphant _non plus ultra_ of the mensuralists. Here, indeed, the rules of measured music preside in iron sway. Not only have the old free ornaments of the early church music been rigorously cramped to a formula and all the kinds of metre reduced to a stiff rule of triple perfection, but the quaint old hymns of the church have been crushed with the gay, mad songs of Paris down hard upon a droning, inexorable tenor which, like a fettered convict, works its slow way along. A reaction was inevitable and it was swift to follow. L. H. FOOTNOTES: [65] See Riemann, _Handbuch der Musikgeschichte_, I², p. 144 ff. [66] See article by Dom Germain in _Revue de l’art chrétien_, 1888. [67] Strict 'imitation’ would be extremely difficult in the tetrachordal system. A subject given in one tetrachord could not be imitated exactly in another, because the tetrachords varied from each other by the position of the half-step within them. Compare, for instance, the modern major and minor modes. The answer given in minor to a subject announced in major is not a strict imitation. If, on the other hand, the answer to a subject in a certain hexachord was given in another hexachord, it would necessarily be a strict imitation, since in all hexachords the half-step came between the third and fourth tones, between _mi_ and _fa_. [68] _Op. cit._, Part II.