5.1The three big functions

In a major key, chords can be grouped roughly into three families:

Tonic function = home / rest

Predominant function = moving away / preparing tension

Dominant function = tension / wants resolution

In C major, the simplest version is:

C → F → G → C

or:

I → IV → V → I

Functionally:

tonic → predominant → dominant → tonic

This is the basic dramatic arc of tonal harmony.