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.

The word madrigal is derived from mandra, a flock, and denoted, originally, a shepherd's song (Pastorale). As formerly stated, early composers often selected for their masses Gregorian chants, or secular melodies. In the madrigal, however, the composition rested upon original invention, thus allowing more variety in form and contrapuntal treatment. In the madrigal, the composer's endeavor was to express through adequate music, the meaning of the poem: he followed closely, with appropriate motives, the sentiment of the different verses. Strict and elaborate canons and fugues were therefore out of place in the madrigal, in which, though seemingly simple in its construction, the composer found ample opportunity to display his mastery in contrapuntal writing. Great variety in rhythm, poetical expression, characteristic melodies, new and striking harmonies, were considered the necessary qualities of the madrigal. It was generally written in three, four, five, six and even more parts, though writing in five parts seems to have been most in favor and use.

The words of a madrigal generally consisted of twelve or fifteen lines, which had no fixed metre, so that the poem appeared more like a free, than a versified recitation. The closing lines often expressed some witty or happy thought like an epigram. The music was governed more strictly by the meaning of the words than it was in the mass, and the counterpoint was more simple and expressive. In some madrigals the voices were treated with exquisite refinement, in a delicate web of counterpoint. Others were composed in simple harmony, note against note. This latter style possessed a diatonic character, out of which the chromatic element of modern music could gradually be developed. The first hints of this new method we owe to Willaert.

Adrian Willaert is considered, if not as the inventor of the madrigal, at least as the composer by whom it was given its first artistic form. It may be regarded as the highest form of chamber-music of those days, written and composed for the refined and appreciative amateurs of the best social circles, principally in Venice and Rome. All composers of repute produced works in this favorite form; among others (beside the two most prominent, Willaert and Cyprian de Rore) Constanzo Porta, Constanzo Festa, Verdelot, Arcadelt, Orlandus Lassus, Orazio Vechi and Luca Marenzio, the last named being the best madrigalist of his time.

There were other favorite vocal forms of a more general character, which were composed according to a chosen metre, to which the poem was afterward set. The name given to this species of composition was modus (still to be found in the Portuguese term for folk-song, modinha) or aer, and from this source was derived the modern name, air or aria, which signifies the manner of singing (as we say a person has a certain air or manner), and does not refer, as many suppose it does, to the medium of song; that is, the sound of vibrating air.

These forms of secular song were inspired, undoubtedly, by the beautiful poetry which enriched Italian literature at that period,—the age of Dante, Petrarch, Torquato Tasso and Bocaccio.

Petrucci published (1504-1508) as many as eight books of Frottole, some nine hundred numbers in all. These are characteristic, though primitive examples of Italian music, and mark the essential difference between that and Flemish music. The latter, like the Gothic architecture of the North, was developed organically from germs or motives, while the former corresponds to simpler forms, the grand curves and arches of Roman churches, within whose walls the pure and elevated harmonies of Palestrina have resounded through the centuries. The innovations which resulted from these new ideas rapidly became popular, and in the course of time, old church modes fell permanently into disuse.