In music theory, a diminished fourth is an interval that has four half steps 
The diminished fourth requires that:
- The interval must be a fourth interval (four note names between the first and the last).
- The interval must have four half steps.
What does a diminished fourth look like?
Here is an example of a melodic diminished fourth (two music notes in a melody) and a harmonic diminished fourth (in a chord):
How to recognize a diminished fourth?
Rule of music theory: All intervals in a major scale starting with the tonic (degree I) are either major or perfect, and only unison, octave, fourth and fifth are perfect (the others are major).
Example with the interval A / D♭:
Let's take the A major scale to have A as the tonic:
From the rule stated above, the interval A / D♮ is a perfect fourth, so the interval A / D♭ is a diminished fourth.
Inversion of the diminished fourth
The inversion of the diminished fourth is the augmented fifth.
Here is an example of a augmented fifth:
Musical examples of diminished fourth
No examples yet, but feel free to send me some examples!
Interval identification game
You will find this interval in my Intervals identification game:
