Augmented and Diminished Intervals

Interval Perfect Intervals Major and Minor Intervals Enharmonic Consonance and Dissonance

Perfect intervals split into no major or minor, and major and minor intervals cannot become "more major". So how do we make an interval wider or narrower still? With augmented and diminished:

Starting point	→	Result
perfect	one semitone wider	augmented (augmented fourth, augmented fifth …)
perfect	one semitone narrower	diminished (diminished fifth, diminished fourth …)
major	one semitone wider	augmented (augmented second, augmented sixth …)
minor	one semitone narrower	diminished (diminished third, diminished seventh …)

One easily confused point: a major interval narrowed by a semitone becomes minor. Only a minor interval narrowed again becomes diminished. So a "diminished third" is not merely a squeezed minor third — it is a genuinely rare interval that sounds close to a major second.

The tritone: one sound, two spellings

The position six semitones up is the special case: it can be written as an augmented fourth (C–F♯) or as a diminished fifth (C–G♭). Both sound identical, but they are spelled and they tend differently:

the augmented fourth expands outward, resolving toward a fifth or sixth;
the diminished fifth contracts inward, resolving toward a third.

In tonal music this interval is one of the strongest engines of motion, which is why it was long nicknamed "the devil in music". The mechanism behind "same sound, different spelling" is covered under enharmonic.

Diagram: the same six semitones, two spellings

Listen: the tritone

Hear the augmented fourth, then hear the very same distance as a diminished fifth. Same pitches, different spelling — the clearest demonstration that names belong to notation while size belongs to hearing.

Common misconceptions

"An augmented fourth and a diminished fifth are two different intervals." Same size, same sound, and they belong together as enharmonic intervals; the difference lives in spelling and tendency.
"Augmented and diminished are purely theoretical." The tritone is one of the strongest engines in tonal music, and a staple of jazz and film scoring.
"A major interval narrowed a semitone is diminished." Narrowing a major interval first yields a minor one; diminished requires one more semitone down from minor.
"A tritone always sounds harsh." Its tension is strong, but in the right harmony it can read as a soft, suspended colour. Context decides.

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Listen in the library

Danse macabre Op.40C12:48Saint-Saëns' Danse macabre in piano score — the core motif is built on an augmented fourth, the source of the whole piece's uneaseDetailsDanse Macabre, S.555C110:20Liszt's solo-piano transcription keeps the interval skeleton, so the same tritone tension can be compared across texturesDetailsDanse macabre Op.40C12:06Another score edition of the same work, useful when checking the enharmonic case of different spellings that sound alikeDetails

All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).

Sources

增/减音程的定义（在纯音程或大/小音程基础上再宽/窄一个半音），属乐理通则
增四度与减五度音数相同（6 半音）、历史上有"音乐中的魔鬼"之称，为通行乐史记载

Used for fact-checking only; all prose is original.

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