Tonic

The home of the key

Of the three main functions the tonic is the resting point towards which everything strives. The subdominant leads away from the tonic and opens up the space, the dominant creates tension and presses back. A large part of all music is built from this triad of functions: away from home, build up tension, back home, from the folk tune to the pop song. The tonic is numbered with a capital in major (I) and in lowercase in minor (i).

Tonic and substitutes

The degree vi, in C major Am, stands in for the tonic: in German functional theory it is called the tonic parallel (Tp), the relative chord of the tonic. It shares two notes with the tonic and colours it more softly. The move V–vi instead of V–I is the classic deceptive cadence, in which the expected tonic is replaced by its substitute. The mediant iii (Em) is also close to the tonic and tints it.

The pop pattern I–V–vi–IV begins on the tonic; all four chords lie close together on the circle of fifths (with its minor ring). More on this on the page One pattern predicts the chords of almost any pop song.

Common mistakes

• Mixing up tonic and root: The tonic is the chord, the root the note.
• Writing it with a capital in minor: The tonic in minor is i, not I.
• Taking every ending for a tonic: A half cadence ends on the dominant, the deceptive cadence on the substitute.