When I was a beginner guitar player, I knew a few open chords: G C A, Am D E, Em. And while playing songs (my guitar lessons were mainly playing songs), I quickly noticed that some combinations of these sounded really good together.
G,C and D sounded “right” together, and so did D, A and G.
But weirdly, blending together G, C, A and D did not.
While playing “Oh Little Town of Bethlehem”, a Christmas Carol, the chords were G, Em, C, D, G and I observed that A was not included. While playing “Mr Postman” by The Carpenters, the chords went G, Em, G, Em, C and D. Again, no A chord.
What was wrong with A?
Yet when we played “Everybody Wants Her” by KC and the Sunshine Band (my guitar teacher was a very hip guy) it went D, A, G, G, A. The A chord was totally fine, but this time C was the kid that got left out of the group.
This baffled my 9 year old brain for a while and I started to guess at possible explanations.
Was it because:
More than 3 chords together start to sound bad?
Songwriters didn’t like to fret 3 fingers on 1 fret to make an A chord, so they left it out?
Dave’s brother told me that A chords sucked and C chords were much cooler?
It turned out that the answer was much simpler (and nothing to do with Dave’s brother).
Chords that sound good together are in a family called a key.
There are 7 of them, and you can pick any chords from this family and play them in any order and they will sound good together.
So how do you find these 7 chords?
First you need to know 2 things:
In a nutshell, the chords in a key are given a number, a specific order and “gender”.
the numbers run 1 to 7 (and are usually written as roman numerals I, ii, iii, IV, V, vi, vii)
the order is alphabetical starting at whatever chord name/letter you assign as the 1
the gender is always: 1-Major, 2-Minor, 3-Minor, 4-Major, 5-Major, 6-Minor, 7-Diminished
So why does G,C and D sound good?
In the key of G major, G is the 1 (I chord), C is the four chord (IV chord) and D is the five (V chord). If you wrote out all the chords to choose from in this key, they would be:
C (IV chord)
D (V chord)
Em (vi chord)
F# diminished (vii chord)
Note the I, IV and V chords are always major and the ii,iii and vi chords are always minor and the vii is diminished.
Why didn’t A sound good with G, C and D?
Because the A chord (full name being A major) is not contained within the key of G - its gender doesn’t match what is required for that key. But Am is, and that would work fine. Try it.
Why do D A and G sound good together but not C?
In the Key of D major, the D is the I chord, G is the IV chord and A is the V chord. As you now know, I, IV and Vs are always Major and so these chords obey the rules of the key. But what about C?
If you wrote out the chords in the key they would be:
D (I chord)
Em (ii chord)
F#m (iii chord)
G (IV chord)
A (V chord)
Bm (vi chord)
C# diminished (vii chord)
So C doesn’t work because it’s not contained within the key of D major.
For 7th chords, the rules of a key work in a slightly different manner but not by much. This video will explain how to find the key and how min7, dom7 and maj7 chords work within one.
Of course, there are always exceptions and many songs break these rules of key by introducing a chord that is not contained within the key but still works.