| Main Interval Name: | diminished fourth |
| Inverse: | augmented fifth |
| Complement: | augmented fifth |
| Other Names: | - |
| Abbreviation: | d4 |
| Semitones: | 4 |
| Interval Class: | 4 |
| Just Interval: | 32:25,[1] 8192:6561, 14:11 |
| Cents Equal Temperament: | 400 |
| Cents Just Intonation: | 427, 384, 417.5 |
In classical music from Western culture, a diminished fourth is an interval produced by narrowing a perfect fourth by a chromatic semitone.[2] [3] For example, the interval from C to F is a perfect fourth, five semitones wide, and both the intervals from C to F, and from C to F are diminished fourths, spanning four semitones. Being diminished, it is considered a dissonant interval.[4]
A diminished fourth is enharmonically equivalent to a major third; that is, it spans the same number of semitones, and they are physically the same pitch in twelve-tone equal temperament. For example, B–D is a major third; but if the same pitches are spelled B and E, as occurs in the C harmonic minor scale, the interval is instead a diminished fourth. In other tunings, however, they are not necessarily identical. For example, in 31 equal temperament the diminished fourth is slightly wider than a major third, and is instead the same width as the septimal major third. The Pythagorean diminished fourth (F, 8192:6561 = 384.36 cents), also known as the schismatic major third, is closer to the just major third than the Pythagorean major third.
In just intonation the usual diminished fourth: the interval C to F, a diatonic minor second plus a pure minor third, or the interval C to F, a minor third plus a diatonic minor second, is 16/15 * 6/5 = 32/25.
The 32:25 just diminished fourth arises in the C harmonic minor scale between B and E.[5]