Text: The distance between any two sounds. In discussing all subjects relating to melody, or to the construction of chords, it is necessary to find names for the various kinds of intervals. Hence, in the earliest treatises on music they are divided into classes. The old axiom that consonance depends on simplicity of ratio naturally led authors to draw a line at the point at which two sounds ceased to be consonant and became dissonant. Among the Greeks, the unison, octave, fifth and fourth were considered more perfect than the third and sixth and other intervals. In medieval treatises an interesting division of intervals into perfect, medium, and imperfect is found; the unison and octave belonged to the first class, the fourth and fifth to the second, the third and sixth to the last. In later works appeared a division which is to this day followed by many writers, namely, into Perfect and Imperfect. This division runs thus: INTERVALS Consonant Perfect 4th 5th 8th Imperfect 3rd 6th Dissonant 2nd 7th All augmented and diminished intervals

See Also: TEMPERAMENT; RATIO; SCALE

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