Subdominant
The subdominant is the fourth degree of the scale and the triad built on it, marked IV (or S). In C major it is F, and the chord F: F–A–C.
The three main chords stand on degrees I, IV and V: the tonic (I), the subdominant (IV) and the dominant (V). In C major they are C, F and G. The subdominant lies a fourth above the tonic (C–F) or, which is the same thing, a fifth below it. In A minor the subdominant is D, the chord Dm: D–F–A.
The subdominant is a step away from home. It is not as tense as the dominant: a calm turn, after which the music usually goes on to the dominant and only then returns to the tonic. The most common chord journey is I, IV, V, I – home, a step away, further away, and home again. It is the backbone of countless songs and of the cadence.
In songbooks you recognise the subdominant by its chord letter: F in C major. The melody notes above it mostly belong to the chord F – F, A, C. To keep the hand still, F is often played in the inversion C–F–A, right next to C.
What it sounds like
The subdominant sounds calm and bright, like stepping aside: after the tonic it opens up space, yet does not demand an immediate return – the dominant does that.
Where it is taught: the studio’s interactive textbook, chapter 9, “Triads: C, F, G”.