parallel fifths

Two voices a 5th apart moving the same direction, the classic counterpoint no-no.

Two voices a perfect fifth apart that move the same direction, staying a fifth apart. Because the fifth is such a hollow, fused interval, the two lines briefly stop sounding independent and collapse toward one, which is why centuries of counterpoint forbid it. The reason is in the math of consonance: a 3:2 ratio fuses.

Learn it: Counterpoint · The math behind music

The one-sentence definition at the top is the same one the Theory Aide extension shows as a tooltip inside Ableton Live. Hover any dotted term for its own.