Tonic
The tonic is the first degree of a scale and the note a piece of music treats as home, the one a phrase can stop on and sound finished.
What is the tonic of C major?
In C major the tonic is C, and the key takes its name from it. The chord built on the tonic is the tonic chord, written I: C–E–G. In A minor the tonic is A and the tonic chord is A–C–E, written i.
The tonic is defined by the music, not by the notes. C major and A minor use exactly the same seven notes, and what makes a piece one or the other is which of them it comes to rest on.
How do you recognise the tonic by ear?
Wait for the end of a chorus, then hum the note that would end the song if it stopped right there. That note is usually the tonic. Two checks:
- It fits under most of the song, because it belongs to three of the key’s most common chords. In C major, C sits inside C–E–G (I), F–A–C (IV) and A–C–E (vi).
- At the end of a section, the bass tends to land on it.
The strongest evidence is the move into it. The dominant chord (G–B–D in C major) holds the note B, one semitone below C, and when it resolves to C–E–G the ear hears arrival.
Is the tonic the same as the root?
No. A root belongs to a chord: G is the root of G–B–D, whatever key you are in. The tonic belongs to a key: there is one per key, and every chord in the key is heard against it. In C major, G is the root of the V chord and is not the tonic.
A second common slip is taking the first note of a song for the tonic. Many melodies start on another note of the tonic chord, often the third or the fifth.
Try it: the drill in What the Degrees Do plays short progressions and asks you to hear which chord settled on home. The full method for songs is in How to find the key of a song.