Functions

The classical diatonic functions are:

1. Tonic (Tonal center)
2. Super tonic (above the tonic)
3. Mediant (a 3rd above the tonic)
4. Subdominant (a 5th below the tonic)
5. Dominant (a 5th above the tonic)
G. Submediant (a 3rd below the tonic)
7. Leading tone (BELOW THE TONIC)

This is fine, but the use of sub & super are inconsistent,
and the actual functions are obfuscated.

I prefer a more modern approach:

1. Tonic
2. Lateral Subdominant
3. Mediant Tonic
4. Submediant
5. Dominant
6. Submediant Tonic
7. Lateral Dominant

Lateral = adjacent to the tonic.

Dominant = most important,
its presence defines the key center (because of the tritone 4-7).
It also means a 5th away from the tonic.

Mediant = in the middle (of dominant or subdominant),
also a 3rd away from the tonic.

The three main functions of chords are expressed:

Subdominant => Dominant => Tonic
(Tension -----> Resolution)

Chords of the same function can often be used interchangeably.

Subdominant	Dominant	Tonic
@-, $	%7, &º	!, #-, ^-