Augmented and diminished · Intervals · Music theory
A major or perfect interval made a half step larger is augmented; a minor or perfect one made a half step smaller is diminished. Two half steps away,…
Augmented and diminished
A major or perfect interval made a half step larger is augmented; a minor or perfect one made a half step smaller is diminished. Two half steps away, doubly augmented or doubly diminished, which are rare.
The qualities form a chain. 2nds, 3rds, 6ths and 7ths go from diminished to minor, major and augmented; the unison, 4th, 5th and octave, from diminished to perfect and augmented.
Four are the most common. The augmented 4th and the diminished 5th split the octave in half; they span three whole steps, which is why the augmented 4th is called the tritone. Next come the augmented 2nd of the harmonic minor scale and the diminished 7th of the diminished seventh chord.
Enlarging and reducing an interval
This is a common exam exercise: given an interval, make it a half step larger or smaller without changing its number. It is done with an accidental on either note; what matters is which way each one moves.
To enlarge, raise the upper note or lower the lower one. To reduce, lower the upper note or raise the lower one. The number does not change, because the letter names stay the same.