The rise in popularity of the monodic, the "one melody" style, involved a sudden decline of interest in the polyphonic school. It is impossible to give with exactness the date of the total disappearance of this later style of writing in Italy. With the gradual introduction of madrigals and through the influence of dramatic music, the hitherto accepted rules of musical construction were subjected to a great change. In the compositions in the old church modes we note, as distinctive traits, an unrelaxing adherence to diatonic scale progressions and a strict preservation of half-tone interval (mi-fa) in all the modes. By this usage each key required, of course, its own special harmonic treatment, and each of the cadences, or endings, differed in character from all the others. The distinctions between the various mediæval keys were, indeed, far more strongly marked than are those which exist between the modern major and minor scales. These great differences led the older church composers to attribute to each of the modes distinct powers of expression; but just as no modern theorist has been able satisfactorily to explain the nature and character of the major and minor keys, so the mediæval composers had widely diverging ideas concerning the modes, and employed them variously, according to their personal preferences. Toward the end of the sixteenth century less strict laws came to be applied to the use of the old church modes, and gradually their peculiar diatonic was wholly lost. Through the efforts of the madrigalists, and especially through the agency of the masters of the Venetian school, the chromatic element became established in music, and the severity and harshness of the church modes greatly lessened. The most common forms of secular music in Italy during the fourteenth and fifteenth centuries were the Frottola, the Villotta or Villanella, and the Madrial or Madrigal. They were all part songs, more or less elaborate, according to the sentiment of the poetry. The Frottole were four-part songs, of a gay and trivial nature, generally popular street songs; but some of them were more earnest and sentimental, being set to good poetry (arcadica). The Villotte or Villanelle were originally peasants' songs, as the name implies. They resembled the frottole, but were more extended and musicianly. The Villotte alla Napoletana were the most artistic songs of this class, but were often sung to frivolous words. The Madrigal was known as early as the fourteenth century, but it did not rise into universal prominence as the representative form of secular music before Willaert's day.