The music of the earliest Christian church as evolved from contemporary practices and systems; the alliance of the Roman liturgy with music; the _Schola Cantorum_--St. Ambrose and liturgical music; his hymns; Gregory the Great and his reforms; the Gregorian antiphonary; sequences and tropes--Progress in musical methods in the northern countries; Hucbald and _organum_; Guido of Arezzo; Franco of Cologne and measured music; growth of part-singing--Early secular music; the Troubadours and Trouvères; Adam de la Hâle; the Minnesingers and the Mastersingers; mediæval secular forms; The early madrigal and its precursors, the _chanson_ and _frottola_; ‘Sumer is icumen in’; relation of folk-music to art-music. I Accustomed as we are in the present age to rapid progress and swift development, it seems difficult to understand why it should have required so many centuries to develop among human beings a feeling for the necessity of more than a single melody or voice-part in music expression. The earliest music of which we have any knowledge is monophonic, a single melody sung by a single voice, or by a number of voices in unison or in octaves. This characteristic prevails not only in the music of primitive races, ancient or modern, but also in the music of those ancient nations that attained a high degree of civilization--Greeks, Romans, Egyptians, Assyrians, Hebrews. The Greeks and Egyptians understood thoroughly the theory of intervals and they possessed an adequate comprehension of intervals in the melodic sense, where tone follows tone. But it seems never to have occurred to them to apply this knowledge of intervals to sounds of different pitch heard simultaneously, certainly never seriously enough to lead them to make experiments in the use of these intervals for the purpose of evolving two or more independent melodies or voice-parts sounding at the same time. Even the crude device of having two melodies move in parallel fifths or fourths, as in the _organum_ of Hucbald, was not employed until the tenth century of the Christian era. And, the principle of discant or added parts to a given melody having been once established, it required nearly six centuries more of constant experimentation with vocal part-writing before there emerged any clear or conscious feeling for what we call harmony or a progression of chord-units. Since the sixteenth century, however, musical progress has unfolded with constantly accelerated pace.