In music, a fourth is an interval spanning four staff positions in the musical notation common in Western culture.
Specific fourth intervals include: Perfect fourth, the fourth spanning five semitones Diminished fourth, a perfect fourth narrowed by a chromatic semitone, thus spanning four semitones Augmented fourth or tritone, an interval of three adjacent whole tones (six semitones)
In addition, fourth in music may refer to: Quartal harmony, harmonic structures built from the perfect fourth, the augmented fourth and the diminished fourth Subdominant, the fourth tonal degree of the diatonic scale