Augmented and diminished intervals
Widen and narrow an interval by a semitone, and name the tritone and its spellings.
A semitone wider or narrower
Any interval can be widened or narrowed by a semitone without changing the note names, using accidentals alone. The number (second, third, fifth) stays the same; the quality changes.
- A perfect interval widened by a semitone becomes augmented; narrowed, diminished.
- A major interval widened by a semitone becomes augmented; a minor one narrowed by a semitone becomes diminished.
The chain of qualities: diminished – minor – major – augmented (for seconds, thirds, sixths and sevenths), and diminished – perfect – augmented (for unisons, fourths, fifths and octaves).
perfect fifth, augmented fifth and diminished fifth above C4
minor third, major third, an augmented third and diminished third above C4
First count the degrees, by the note names, ignoring accidentals. Then count the semitones and compare with the "normal" size for that number: that gives the quality.
Practice: A wide second
Practice: A narrow seventh
Practice: Build augmented and diminished intervals
One sound, two spellings
Augmented and diminished intervals often sound like familiar ones but are written differently. They are enharmonically equivalent.
- augmented fourth and diminished fifth have six semitones each. This is the tritone: three whole tones, exactly half an octave.
- augmented second sounds like minor third, and diminished seventh like major sixth.
The ear cannot tell them apart: the key the notes belong to decides which spelling is right.
augmented fourth and diminished fifth: they sound the same
augmented second and minor third: they sound the same