The chords that substitute · Harmonic functions · Music theory
The other degrees group around these three according to the notes they share. VI and III resemble the tonic because they have two notes in common with it;…
The chords that substitute
The other degrees group around these three according to the notes they share. VI and III resemble the tonic because they have two notes in common with it; II resembles the subdominant; and VII, the dominant, because it contains its tritone. So one can take the place of another without breaking the sense of the phrase.
A substitution changes the color, not the function, but it only works if the melody allows it. A melody resting on G can sit over C major or E minor, but not over A minor without adding another color. So always check it against the note sounding on top.