Fourths

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

Diminished fourth, 2 whole steps or 4 half steps

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

Augmented fourth, 3 whole steps or 6 half steps

Identifying fourths

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

• the interval is a perfect fourth if all the notes are natural, with the exception of the fourth F-B, which is an augmented fourth.

 If there are accidentals you should identify the interval without accidentals and then analyze the effect of the accidentals.

 Example: G-C#:

Another example: C#-F#:

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

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English version revised by Sue Talley