In addition to [[interval size|numerical size]], each interval has a specific quality that distinguishes it from other intervals of the same size but with a different number of half steps. Intervals can be grouped into two classes according to their possible qualities: (1) *perfect intervals* and (2) *major–minor intervals*. ## Perfect Intervals The perfect intervals include unisons, fourths, fifths, and octaves and their corresponding compound intervals. If we expand a perfect interval by a half step, it becomes **augmented**. If we contract it by a half step, it becomes **diminished**. ![[example interval quality perfect intervals.png]] As shown in **Example 1**, a perfect interval may be expanded into an augmented interval either by raising the upper note or lowering the bottom note a half step. **Example 1.** Perfect fifth to augmented fifth. ![[example interval quality perfect intervals augmented.png]] Conversely, as shown in **Example 2**, a perfect interval may be contracted into a diminished interval by lowering the upper note or raising the bottom note a half step. **Example 2.** Perfect fifth to diminished fifth. ![[example interval quality perfect intervals diminished.png]] ## Major–Minor Intervals The major–minor intervals include seconds, thirds, sixths, and sevenths, and their corresponding compound intervals. A major interval is one half step larger than a minor interval of the same numerical size. If we expand a major interval by a half step, it becomes augmented. If we contract a minor interval by a half step, it becomes diminished. ![[example interval quality major-minor intervals.png]] **Example 3.** Major, minor, diminished, and augmented sixths. ![[example interval quality major-minor intervals sixths.png]] > [!NOTE] Important! > Unisons, fourths, fifths, and octaves are never major or minor. Conversely, seconds, thirds, sixths, and sevenths are never perfect.