Previously we looked at the numeric section of an interval, which provides a rough measurement of the distance between two pitches. The numeric portion of an interval can be thought of as being similar to the numbers on a ruler or the hour hand on the clock.
The quality of an interval provides a more precise measurement than the numeric portion alone. The quality can be thought of as the marks between numbers on a ruler or the minute hand of a clock.
Musical intervals have two sets of qualities:
The quality set that is applied to an interval depends upon the numeric portion of the interval, as follows:
Noteworthy– Since Diminished and Augmented appear in both quality sets, any interval may be diminished or augmented