What Is the Subdominant?
What Is the Subdominant?
The subdominant is the fourth scale degree of a key, and the chord built on it — the IV chord. In C major, the subdominant note is F and the IV chord is F major. If the tonic is home and the dominant is maximum tension, the subdominant is the departure: the "we've left home, something's in motion" sound.
The middle of the tension arc
Classic harmony moves in an arc: I → IV → V → I — rest, departure, tension, resolution. Listen to a 12-bar blues: the move to the IV in bar 5 is the song visibly leaving home, and the V in bar 9 is what points it back. Thousands of common progressions are variations on this arc, which is why I, IV, and V alone can play most of the folk, blues, and rock canon.
Name and neighbors
"Sub-dominant" doesn't mean "weaker dominant" — it means below the dominant: a fifth down from the tonic, mirroring the dominant's fifth up. (C down a fifth is F; C up a fifth is G.) The plagal or "Amen" cadence — IV going straight to I — is the subdominant's signature move, softer than V–I.
In Roman numeral terms, chords with subdominant function include IV and its relative, the ii chord.