 Chord building        Tonic Sub-dominant Dominant
If you're confused, see theory.

# Chord building

There are 7 basic chords in the Major scale.
The colors show the stability of each note (compared to the root note).

Stable        Unstable        Very unstable To make a chord, pick a root note.  Skip the next note in the scale.  Use the next note.  Skip a note.   Use a note.

These chords make a key.    Re-number each chord. # Dominant  Subdominant  Tonic

These terms explain how chords interact in a key.
Some chords are stable and some chords are unstable.  Tonic is the 1 Chord.
It contains all three stable notes
.    The Tonic can also be the 1 Note.

Chord 1

=
1  3  5

Tonic Function
These chords contain two stable notes.

Chord 6

6  1  3
Chord 3  =    3  5  7

Chord 3 is less stable than Chord 6 because it contains the 7 (the leading tone which wants to resolve to 1)

The 6 or 3 chords can change function depending on where they're located in a chord progression.

Subdominant
These are less stable because they contain less stable notes.

Chord 4  = 4  6  1
Chord 2
=  2  4  6

Chord 4 is less stable because it contains the 4 and one stable note 1
Chord 2 is less stable then Chord 4 because it contains the 4 and no stable notes.

Dominant
These chords have a strong "need" to resolve.
They dominate the chord progression.

Chord 5  =    5  7  2
Chord 7  =    7  2  4

Chord 5 is less stable because it contains 7 and 2
Chord 5 resolves to Chord 1 because of 7 (the leading tone) and the relationship of the 5 to the root note (1 or tonic).
See
overtones in a note.

Chord
7 is least stable
because it contains the most unstable tones, (7  2  4).
It resolves to Chord 1, because of 7 and because the natural* resolution of (7  2  4)  is  (
1  3  5).
Chord 7 also has a b5 instead of a 5.  This interval (the tritone) is the most unstable interval and "requires" resolution to Chord 1

* This differs from the natural resolution of each note.  This is the natural resolution for the chord.

Coming soon:
Harmonic choices
most similar- smoothness   least similar
vi and 3 as chameleons.

# Chords relative to themselves

Imagine this group of seven chords is the solar system.  They all revolve around the sun.  The sun is the tonic.
However, each chord is a separate planet.  It's stable to itself, with systems of it's own.

Each chord by itself, is stable.
(with the exception of Chord 7)

If you start by playing the 5 chord (a tense chord) it won't sound tense until you play more chords that define it as the 5 chord.
Until then it will sound very stable, since it's a Major chord. 