Few madrigals whose composition antedate the invention of printing have been preserved. But all authorities agree that even in its earlier stages it was composed for three or more voices in the prevailing church modes. Throughout its best period, which closed practically with the sixteenth century, it maintained the characteristic of being sung without instrumental accompaniment of any kind.[12] The association of concurrent parts with plain-song undoubtedly suggested similar treatment for secular melodies, and the troubadours and trouvères were probably the first to put this suggestion into practice. But they passed out of existence before the art of discant had progressed beyond its first stage of infancy and further development of polyphonic secular music was left in the more skilled hands of the scientifically trained musicians of the church. The madrigal, or more strictly speaking its predecessors, was forthwith adopted by the church composers, who treated it with much tenderness and lavished on it all the learning and technical skill they could command. Since these composers, however, were so thoroughly imbued by training and experience with the characteristics and idioms of church music, we find no essential differences, as far as the music is concerned, between the madrigal and its ecclesiastical counterpart, the motet (see Chapter II). These two forms have maintained an almost exact correspondence with each other in each successive stage of their musical development. The only real difference lay in the nature of the words employed, those of the madrigal being always secular, those of the motet, sacred. While the madrigal was just as polyphonic as the motet and followed the same general laws of musical construction, it was in lighter vein and in simpler style to suit the secular spirit of the words. The ponderous and solemn character of the motet was avoided, the contrapuntal parts became more plastic and expressive in conformity with the sentiment of the words. These freer and more expressive qualities in the madrigal were eagerly seized upon by the dramatic composers of the seventeenth century, during which period the madrigal was a regular feature of the opera. Dr. Stainer enumerates the following essential qualities of the true madrigal: themes suitable in character to the words, variety of rhythm, short melodic phrases, imitation and counterpoint.