Sevenths can be major, minor, augmented or diminished. Below you can that the number of steps determines the quality of the interval:

Major seventh, 5 1/2 whole steps or 11 half steps:

Minor seventh, 5 whole steps or 10 half steps:

Diminished seventh, 4 1/2 whole steps or 9 half steps:

Augmented seventh, 6 whole steps or 12 half steps:

Identifying sevenths

The easiest way to identify the quality of a seventh is by inverting the interval and identifying the resulting second. For example, the interval C-B:

1. Seventh interval
2. Becomes a second when inverted
3. A minor second means the seventh is major (see inversion of intervals)

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