Perfect Fifth

Names and symbols

Perfect Fifth is written P5, 5P: the letter is the quality, the number the size. Chord formulas on this site write the number first, as tonal does.

"Perfect" is not praise. Unisons, fourths, fifths and octaves take the qualities perfect, augmented and diminished, never major or minor, because their inversions keep the same quality. A fourth one semitone narrower than perfect is diminished, not minor.

How it sounds

A perfect fifth spans 7 semitones: C – G. Its frequency ratio is almost exactly 3:2, the simplest ratio after the octave, so the two notes share a great many overtones and lock together with no beating at all.

It is the first interval you hear in the overtone series above the octave, which is why it sounds less like two notes than like one note made fuller. Play any pitch and a fifth is already quietly present in its own harmonics.

How composers use it

Every major and minor triad is a fifth with a third inside it. Stack fifths and you generate the circle of fifths, and with it the key signatures and the strongest of all root motions.

On guitar the fifth alone is the power chord: no third, so neither major nor minor, which is exactly why distortion suits it — there is no third to turn muddy. Open fifths in a bare texture read as archaic or vast, which is why they carry so much fantasy scoring.

Its inversion is the Perfect Fourth, and the two together span an octave.