The foundation of all the art-music of the Middle Ages was the chant; and the science of music concerned itself wholly with the addition of more or less free and independent parts to the chant-melodies. Musical invention, however, was limited entirely to these accompanying parts. Until probably the fourteenth century or even later, composers as such were unknown. Since music in the church was never considered apart from the liturgy to which it was wedded, not only did the melodic form of the chants themselves (that is, their rising and falling inflections of pitch) follow quite closely the natural rhetorical utterance of the words of the liturgy, being an intensification of the natural values of forceful speech, but for several centuries after the principle of polyphony was thoroughly recognized the intricate church compositions, such as the masses and motets, were constructed by using the liturgic chants as subjects and adding free parts to these. At first the principal melody (subject) was taken from the chant books; but in course of time secular songs of the day found their way into the choral parts, either as the principal melody to which other parts were supplied or as an accompanying part to a given plain-song melody. The secular words, frequently of questionable moral quality, were often carried along with the melodies into the sacred company of actual ritual-music and the singers found such a combination neither irreverent nor incongruous. It was quite analogous to the custom, common among the early painters, of painting the portraits of such ordinary mortals as wealthy purchasers or patrons on the same canvas with saints or apostles, or even with the Madonna. The church authorities frowned upon mingling secular and sacred elements in ecclesiastical music in this manner, and the practice, so common in the fourteenth and fifteenth centuries, led to such gross abuses that it was finally suppressed.