Consonance and dissonance
Sort intervals into stable and tense ones and recognise them by ear.
Smooth and tense
Listen to two notes sounding together. Some intervals blend into a soft, calm sound: these are consonances. Others sound sharp and tense, as if asking to move on: these are dissonances.
A dissonance is not a "bad" sound: music moves forward precisely through tension that resolves into rest.
Consonances: a fifth, a major third, an octave
Dissonances: a major second, a major seventh, a tritone
Practice: Calm or tense?
Three groups
- Perfect consonances: the perfect unison, octave, fifth and fourth. They sound open and clear; the notes nearly merge.
- Imperfect consonances: major and minor thirds and sixths. Full and warm, they carry harmony.
- Dissonances: seconds, sevenths and the tritone. Sharp and tense.
The fourth sits on the border: alone it sounds stable, but in harmony it often behaves like a dissonance.
To tell them apart by ear, imagine singing both notes calmly together with someone else. A third or a fifth is easy to sing; a second grinds, the voices get in each other's way.