This is a simple lesson for the novice on the subject of Basic Primary and Secondary Chords or what is also sometimes known as the 6 Scale Chords.
So why do some chords work well together and some dont ?
To answer that question the first thing we need to do is to take a look at the Major Scale, we'll use C as an example, the Roman Numerals are used to represent the Major Scale positions.
ROOT Sub-Dom Dominant Octave
I II III IV V VI VII VIII
C D E F G A B C
THE 3 PRIMARY CHORDS @ I-IV-V ( C-F-G )
The reason why some chords work is because they belong to a key, in this case C and the most important chords in a Major key are the I Root Chord, the V Dominant chord and the IV Sub-Dominant Chord ( as indicated above ) if you look at the diagram you will see a C at the I and VIII, and in the middle the F and G, by observing the symmetry you get an idea of the magnetic influence of the I and VIII and how it pulls through the centre. All chords want to find their way "home" to the I Root eventually and have varying degrees of magnetism, pulling and pushing their way around the whole scale, none more so than the V and IV, so this is why we call the I, IV and V The 3 Primary Chords, In C @ C, F and G, if you use the Roman numerals you can take a key e.g., G so G is I, A is II thus C is IV and D is V etc etc.
THE 3 SECONDARY CHORDS @ VI-II-III ( Am-Dm-Em )
So we have the 3 most commonly used chords in music but they are all major and where is the Minor?
The first thing we need to do is look at the scale again, and focus on the VI Chord, as this is known as the Relative Minor Root Position, all Major keys have a Relative Minor Key that uses exactly the same notes,& vica versa all minor keys have a relative major key.
So the VI is the Relative Minor Root position to C or "i" which is A minor. If we play in the key of A minor A is i, B is ii, C is iii (Relative Major), D is iv and E is v, hence the 3 minor secondary chords Am,Dm and Em.
THE 6 SCALE CHORDS IN 2 KEYS C AND G
I II III IV V VI VII VIII
C C Dm Em F G Am
G G Am Bm C D Em
Where I have indicated with a * these chords also work nicely as 7ths.
So try the 6 Scale Chords in any order you like and experiment.
PRIMARY CHORDS SECONDARY CHORDS
In C C - F - G and / or G7 Am - Dm - Em and / or E7
in G G - C - D and / or D7 Em - Am - Bm and / or B7
Just remember that the 6 scale chords belong to both C AND A minor, and both keys have exactly the same notes, but with root positions in different places. When you have spent some time on the 6 Scale chords you can investigate the last chord that completes the set the VII which is Diminished.
I hope this helps....Andy