The subdominant (the 4th degree) is the “departure” from the tonic before the return via the dominant. The T-S-D-T formula (tonic-subdominant-dominant-tonic) is the fundamental harmonic pattern of all classical music.
Subdominant harmony is often associated with prayer, reflection, and nature: the famous “Amen cadence” (IV–I) closes many church hymns. In 1960s–70s rock (The Beatles, Pink Floyd), the subdominant becomes the basis of psychedelic sonority, replacing the expected dominant with a subdominant chord.
The subdominant is the fourth degree of the scale, and together with the tonic and dominant it forms the three “pillars” of classical harmony. Unlike the dominant, which pulls sharply back to the tonic, the subdominant opens space, “leads away” from the centre, and so is often linked with breadth, contemplation, and prayer. The subdominant seventh chord built upon it and the related “Neapolitan” harmony enrich a work's palette of tensions.
