Jazz Guitar Theory

How are guitar chords built?  What makes a chord minor or major? If you're not sure about this then read on ... Some background theory makes a tremendous help when learning how to play guitar chords. Let's get started with the C major scale : C Major Scale C    D    E    F    G    A   B 1    2    3    4    5    6   7 Triads (a chord that is built with 3 notes) and seventh chords (chords that are built with 4 or more notes) are based on thirds. There are 2 kinds of thirds (or 3rds) : minor third interval of 3 half steps symbol : minor 3rd major third interval of 4 half steps symbol : major 3rd Let's start by stacking 2 thirds on the 1 (first note) of the C major scale: C    E    G 1    3    5

The result is a C major triad or C.  From C to E is a major 3rd and from E to G a minor 3rd: every major chord has this structure.
The thing to remember here is what we call the chord formula for major chords: 1 3 5
Another thing to remember : another name for the 1 of a chord is the root.

Let's do the same for the 2 of the C major scale :

D    F    A

1    b3   5

The result is a D minor triad or Dm.  From D to F is a minor third and from F to A is a major third : every minor chord has this structure.
Again the thing to remember is the chord formula for minor chords : 1 b3 5

Now we're going to skip a few notes and stack thirds on the 7 of the C major scale :

B    D    F

1    b3   b5

The result now is a B diminished triad or Bdim.  From B to D is a minor 3rd and from D to F is also a minor 3rd : every diminished triad chord has this structure.
So the chord formula of diminished chords is : 1 b3 b5

I'll summarize and complete the other notes of the C major scale :

	Notes	Formula	Chord Name	Symbol
1	C   E   G	1    3   5	C major	C
2	D   F   A	1   b3   5	D minor	Dm or D- or Dmin
3	E   G   B	1   b3   5	E minor	Em or E- or Emin
4	F   A   C	1    3   5	F major	F
5	G   B   D	1    3   5	G major	G
6	A   C   E	1   b3   5	A minor	Am or A- or Amin
7	B   D   F	1   b3  b5	B diminished	Bdim or B°

There are 2 ways to construct chords

1. The first way starts from the major scale.

1. Find the major scale of a given key. If you're not sure how to do this, go here: How To Construct a Major Scale. If you need to find for example the notes of a Gm chord then find the G major scale : G A B C D E F#
2. Construct the major chord : 1 3 5. In our G major example that would be : G B D
3. Apply the chord formula to the major chord. The chord formula for minor chords is 1 b3 5. This means the 3rd of the major chord has to be lowered half a step : G Bb D

2. The second way involves some memorization and will be explained in part 4, after we coveredseventh chords and tensions.

Reference: http://www.jazzguitar.be/jazz_guitar_chord_theory.html