Often I’m asked why certain chords relate to each other, what their relationship is to a given scale, how to string chord progressions together and why two chords often work together. These are common questions, whether you’re songwriter, producer, in a band or a soloist, as it can stifle song writing blindly attaching chords together and hoping for the best. I’m going to take a look at what chords we can extrapolate from the key we’re working in.

Western music has keys and scales that broadly govern how we organise our sounds. Without delving too far into the Harmonic series or Equal temperament there are basically a finite number of chords that will work ‘well’ together, both sounding ‘pleasing’ and working on deep mathematical levels (to understand that, you’ll need to read up on Pythagorean Intervals).

These types of chords are the ones you’ll hear in 95% of written western music. From barbershop quartets to Shostakovich, from the Beatles to Brian Eno there are ‘correct chords’ that are used in their compositions.

N.B I’m recoiling at the constant use of the quotation marks. What sounds good in music is largely subjective but we’re talking about chord progressions that would sound correct to a layperson. There are plenty of examples of popular music that step outside of these simple rules but that’s not a topic for now.

Diatonic Chords

There are 7 chords related to each scale. The ones that appear most commonly are the I, IV, V and vi. In C, this would be C, F, G and Am. If you are unfamiliar with the Roman Numeral system, keep an eye out, as something will be going up on it soon.

The chords in C major are as follows:

Chord Notes Score
C major C E G C major
D minor D F A D minor
E minor E G B E minor
F major F A C F major
G major G B D G major
A minor A C E A minor
B minor flat 5 B D F B minor flat 5

If you read each note of the chord vertically you are reading the C major scale starting from a different place.

Each chord is built from two intervals: major third (4 semitones) and minor third (3 semitones). Any combination of major and minor thirds gives you any chord… well, most of the useful ones anyway. The major chords are built root, major third, minor third; and the minor are built root, minor third, major third.

Major chord = root > 4 semitones > 3 semitones

Minor chord = root > 3 semitones > 4 semitones

Using the above, C major is C, E and G whereas C minor would be C, Eb and G. The root and fifth are the same (as 4+3 is the same as 3+4).

The only exception in diatonic harmony is the B minor 7 flat 5 chord, which is root, minor third, minor third.

7th Heaven

Let’s add a note on top of the chords we extracted earlier. If you were to take the next leap in the scale, say if we were to add another third above, we would get the following:

Chord Notes Score
C major 7 C E G B C major 7
D minor 7 D F A C D minor 7
E minor 7 E G B D E minor 7
F major 7 F A C E F major 7
G dominant 7 G B D F G 7
A minor 7 A C E G A minor 7
B minor 7 flat 5 B D F A B minor 7 flat b5

(Notice the G chord is not a major 7)

Some chords have had a major third added, some a minor, this depends on what fits with the key we’re in. In this case, C major. Anything inside this key could be described as diatonic.

Here you’ll see major 7 chords are built root, major third, minor third, major third; minor 7 chords are root, minor third, major third, minor 7. The exceptions here are G7, root, major third, minor third, minor third; and B minor 7 flat 5 which is root, minor third, minor third, major third.

The reason we don’t have G major 7 is that the 7th degree of a G major scale is F#, which is not in the key of C major, hence it being F natural. Once you’ve nailed this concept you’ll find that chord are really quite simple to work out in any key.

More Extensions

The above ‘leap-frogging’ process can take you further still, adding 9ths to chords. Again we’re adding a diatonic third interval above. From here on in

I’m going to write the chords as I would write them on a song chart, so C∆9 rather than C major 9, D-9 rather than D minor 9 etc etc. This is just a form of shorthand and it’s simple to get to grips with eventually.

If you’re unfamiliar with these chord names, please refer here.

Diatonic Chords (9s)

Some of you may be wondering why these chords are called 9ths when they are adding the 2nd degree of their parent key. The way I learnt and understood it is that if you imagine 2 octaves of the scale laid one after another, numbering them 1-7 and beyond, the 9th degree would be D.

Chord extensions tend to appear in the 2nd octave (though this is not a rule, just a common occurrence). This applies for the 2nd degree (known as 9), the 4th degree (known as 11) and the 6th degree (known as 13). So you might see C-9, G13, B11 etc.

The quick way to discern the extension is to minus 7, e.g. 9-7=2, meaning that the 9th is the 2nd degree of the scale. This can be confusing so if you have any questions leave a comment and I’ll do my best to explain it a little further.

Lastly you might notice that the Em7(b9) seems to buck convention – why is it not E-9? Similar to the G7/G∆7 quandary we discussed above, this is because in the key of E minor the 9th degree would be F#, not F. So what you’re doing here is, in a sense, flattening the 9th. The same applies with the B-7(b5, b9) chord.

Conclusion

These chords are what can be extrapolated from a diatonic major scale. For me, they’re the first port of call when I’m looking where a progression should go.

Of course I don’t want to discourage anyone from using non-diatonic chords (chords not found in the scale) because they add flavour and personality to vanilla progressions and they’re mandatory when modulating to other keys.

It’s important to use your ear when composing but knowing which chords are likely to work can speed up the process and solve problems when your ear might be letting you down.