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Interval quality

The quality of an interval is its distinctive sound, based on the number of half steps between the two pitches. The terms used to label interval quality are:  major, minor, perfect, diminished and augmented. Study the following chart.

The terms on the left side of this chart (augmented, major, minor, diminished) are used to define 2nds, 3rds, 6ths and 7ths. The terms on the right side (augmented, perfect, diminished) are used to define unisons, 4ths, 5ths, and octaves. Notice that the terms augmented and diminished are used for all interval number sizes. On the other hand, there is no such interval as a Major 5th, nor is there a Perfect 3rd.

As you go up on the chart, the size of the interval increases by one half step; vice-versa, as you go down on the chart, the size of the interval decreases by one half step. Thus, a major sixth (labeled "M6") is 1/2 step larger than a minor sixth (m6); a perfect fifth (P5) is 1/2 step smaller than an augmented fifth (A5).

If you increase the size of a diminished seventh (d7) by a half step, it becomes a:

If you decrease the size of an augmented fourth (A4) by a whole step, it becomes a:

If you decrease the size of a major third (M3) by a half step, it becomes a: