Guitar chord theory

Jan

17

≡ Category: Music Theory | ≅

This lesson discusses the structure of chords. Chords are easily explained through the use of the Major scale. Although scales will be introduced in more depth later, for ease of use we will refer to the major scale in the key of C. A scale is merely a sequence of notes in a particular key. The C major scale is convientient to use as its layout is very simple in that it contains no sharp or flat notes. The layout is as follows:

C, D, E, F, G, A, B (C)

Just C through to B then the notes are repeated again, easy !

If you’ve read through and understood the lesson on notes (do this first) then you’ll realise that there is a set pattern of intervals between the notes:

Note	C		D		E		F		G		A		B		(C)
Interval (in semi-tones)		2		2		1		2		2		2		1

It is this interval which defines the major scale. So if you are starting of in a different key, to get the other notes present, you just calculate them using the same interval. Just for reference, the following table shows all twelve keys with the corresponding notes of their major scale. I’ve just stuck to using sharp notes, but remember, a C# is a Db, etc.

Note

1st

2nd

3rd

4th

5th

6th

7th

8th

C Major

(C)

C# Major

D Major

D# Major

E Major

F Major

F# Major

G Major

G# Major

A Major

A# Major

B Major

Interval (in semi-tones)

So you’ve managed to get all twelve major scales aswell, thrown into one lesson !

So how does this relate to chord structure ?

Each chord type has a specific structure, or formula that describes it based on the major scale from the same key. This is best described using an example. The formula for a major chord, is to take the 1st, 3rd and 5th notes from the scale of the same key. So for the chord of C Major, the notes required to make up the chord are C, E & G (taken from the above table), A# Major would be (A#, D, F).

N.B the 1st of a chord is also called the "root" of the chord.

So all you need to know is all the formulae for all the different chords and you can make them up yourself. So if you take a look at the table below (which I prepared in the oven earlier) you’ll find most of the formulae you’ll ever need (trust me unless your a serious session musician or something, you probably wont ever use even a half of them, or atleast I dont).

I’ve added in details to the table which explain certain developments, if you study it close enough you’ll see a simple pattern emerging. Realistically, you should be able to remember all the formulae that you’ll need and you can always trace out all of the major scales, by writing down C first and then using the same intervals, to get the rest. So now you hold in your head all the chords you’ll ever need.

It may be worth going through a few chord shapes that you know just to verify all of this, by working out what notes are in the chord and see how they compare to the formulae below.

Chord	Details	1^st	2^nd	3^rd	4^th	5^th	6^th
Major	Always include 1^st, no flats or sharps	1	3	5
6		1	3	5	6
Major 7		1	3	5	7
Major 9		1	3	5	7	9
7	Any chord after and including 7^th has a flat 7^th	1	3	5	b7
9		1	3	5	b7	9
13		1	3	5	b7	9	13
Minor	Minor always indicates a flat 3^rd	1	b3	5