So much technical detail will be forgiven by the reader who can at all realize how profoundly the entire history of music has been affected by these acoustic and physiological facts. We have already seen how folk-music slowly wrought out the complex metrical forms based upon time grouping. In the same way, ecclesiastical music wrought out, slowly and laboriously, the harmonic and melodic forms that were based upon pitch-grouping. For a long time vocal utterance was defined only by certain simple intervals like the fall of the fourth, which formed the cadences of Greek dramatic recitation and of mediæval Christian intoning. Gradually ornamental notes were introduced as approaches to the final note; these were varied in pitch, and new ones added, until finally there resulted the ancient modes, precursors of our scale. Then, when two melodies began to be sung at once, the intervals of the octave, fifth, and fourth were again called into requisition, and made the bases of primitive harmony. In the old Organum of the Middle Ages, two voices, a fifth apart, gave the same melody, just as with the Greeks, in the process called «magadising,» two voices sang the same tune, an octave apart. So, step by step, pitch relations were perceived and utilized. In all stages of the long progress, whether the interval chosen was the octave or the fifth or the fourth, and whether the tones were sounded in succession as a melodic step or simultaneously as a chord, the guiding principle was the same; tones were grouped together which had pitch-form, which had partial tones in common and others not in common. A harmonic form, like a metrical form, was always a cluster of tones that could be both associated and distinguished.