Augmented & Diminished Intervals
Push a major or perfect interval a semitone wider and it becomes augmented. Squeeze a minor or perfect interval a semitone narrower and it becomes diminished.
Stretching and squeezing
An augmented interval takes a major interval (from the 2nd/3rd/6th/7th family) or a perfect interval (unison/4th/5th/octave) and widens it by one semitone. A diminished interval takes a minor interval or a perfect interval and narrows it by one semitone. The interval number stays exactly the same — only the quality label and the semitone count shift.
The enharmonic overlap
Some augmented and diminished intervals land on the exact same semitone count as another spelling entirely. The most famous case: an augmented 4th and a diminished 5th are both 6 semitones — the tritone. Which name you use depends on the musical context and the letter names actually involved, not just the sound. Spelling matters for reading and part-writing even when the ear can't tell the difference.
Common questions
What is an augmented interval?
A major or perfect interval widened by one semitone — a major 3rd widened becomes an augmented 3rd.
What is a diminished interval?
A minor or perfect interval narrowed by one semitone — a perfect 5th narrowed becomes a diminished 5th.
Why do augmented 4ths and diminished 5ths sound identical?
Both equal 6 semitones — the tritone. They're the same pitch distance but spelled differently depending on context.
How do I know whether to spell something as augmented or diminished?
Spelling follows the letter names and musical function involved, not just the sound — even when two spellings share a semitone count.
Train your ear on the edge cases
Melody Monkey's Ear Training tool includes augmented and diminished intervals alongside the basics.
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