Fourths can be perfect, augmented or diminished. Below you can see that the number of steps determines the quality of the interval:

Perfect fourth, 2 1/2 whole steps or 5 half steps:

Augmented fourth, 3 whole steps or 6 half steps:

Diminished fourth, 2 whole steps or 4 half steps:

Identifying fourths

When analyzing the quality of a fourth we should know that:

• all fourths in which both notes have the same accidentals are perfect, except for F-B which is augmented. If there are accidentals, it is recommended to analyze the interval without the accidentals and then see how the accidentals affect the interval.

Example: G-C#:

Another example: C#-F:

Identifying fourths by counting whole and half steps is slow and confusing.

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