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Where do chords come from?

By Dave Marshall

Have you ever wondered why certain chords are used in a particular key? Have you ever pondered upon which notes go to make up a particular chord? With just a tiny introduction to music theory, we can work out the notes for any major scale, the chords that belong to any major key and the notes that make up each chord. This will allow us to understand why we fret certain strings to make a particular chord and it will also enable us to discover new chord shapes in different tunings.

Scales

We are all familiar with the sequence: doh, ray, me, fah, so, lah, te, doh. These are the 8 notes that make up a major scale.

Between each pair of notes of a major scale we must have two semitones (or half steps), except from 3 to 4 and from 7 to 8. These must be separated by one semitone.

Using this simple rule we can construct any major scale. Let’s take a look at the C major scale:

Notes occur with letters from A to G. We begin our scale with the root note, in this case C, and step through the alphabet, restarting with A when we reach G. We can see in the table that position 3 is E and position 4 is F. These notes are naturally a semitone apart. Likewise we find the note B at position 7 and note C at position 8. These two notes are also a semitone apart. All of the other notes are naturally two semitones apart. So in the C major scale we can see that our simple rule is met.

Now let’s look at the D major scale:

We begin with the root of the scale, D, and count up from there.

However, without the necessary adjustments, we will find that we do not have the required semitones from 3 to 4 and 7 to 8. To achieve the correct spacing we have to raise the 3^rd note from F to F# in order to create two semitones from position 2 to 3. This also gives us the necessary single semitone from 3 to 4. Similarly, by raising the 7^th note from C to C# we create two semitones between positions 6 and 7, and one semitone from 7 to 8.

Consider the A major scale: 

To achieve our correct spacing of notes we find that we have to raise note 3 to C#, note 6 to F# and note 7 to G#.

Consider the G major scale: 

For the G major scale, we can achieve the correct note spacing by just raising note 7 to F#.

Chords of a major key: I, IV and V

The primary major chords of a key are found at positions 1, 4 and 5 of the scale. So, for the key of C, we get C at position 1, F at position 4, and G at position 5. For the key of D, our positions 1, 4 and 5 give us D, G and A. For the key of A, we get A, D and E and for the key of G we get G, C and D.  In western classical notation chords built on the scale are numbered with Roman numerals.i.e. I, IV, and V and we normally play the V chord as a flattened 7^th, typically just called the “7^th”. So for the key of G we have G, C and D7.

Notes that form a major chord: 1, 3 and 5

The notes that make up a major chord are found at positions 1, 3 and 5 of the major scale. For example, a C major chord is made up of notes C (the root), E (third) and G (fifth). Likewise, a D major chord consists of D, F# and A. It doesn’t matter in which order we arrange the three notes; it is still the major chord. In fact, by rearranging the notes, we form chord “inversions”. Providing that you know how each string of your instrument is tuned, it is a simple matter of finding the 1, 3, 5 combinations in order to uncover any chord that you need.

How to construct a chord

Assuming that we have our banjo in standard G tuning, our strings will be tuned as follows: 

5^th string is G
4^th string is D
3^rd string is G
2^nd string is B
1^st string is D

If we look at our G scale, we see that notes 1, 3 and 5 are G, B and D, so our open strings are tuned to the notes of a G chord; hence the name “G tuning”. When we strum the open strings we hear a G chord.

Let’s construct a C chord. First we need the notes that make up a C chord. Looking at the C major scale we see that notes 1, 3 and 5 are C, E and G. Our 5^th string and our 3^rd string are tuned to G so they are valid for a C chord. However, our 4^th and 1^st strings are tuned to D, which is not part of a C chord. Most fretted instruments are designed so that each fret represents a “semitone” or half step. So, by fretting both the 4^th string and the 1^st string at the 2^nd fret, we raise the pitch of those strings from D to E. Lastly we need to fret the 2^nd string at the first fret in order to raise the pitch one semitone from B to C. Hey presto, we have our C major chord.

For the V chord of our I, IV, V triad for the key of G major we normally play the “seventh” i.e. D7 . To construct a D chord we look at the D major scale and find that the 1,3, 5 notes are D, F# and A. Our 4^th and 1^st strings are already D. We fret the 3^rd string at the second fret in order to raise it from G to A. Finally, to get our “seventh” chord shape, we need to add the “flattened 7^th” note of the scale. The 7^th note of the D scale is C#, so a flattened 7^th note would be C. We get this by fretting the second string at the first fret.

To summarise, the same procedure can be followed to find any chord shape for any key, simply by finding the I, IV, V triad of the key from its scale and then finding the 1, 3 and 5 notes of each chord on the fretboard. I hope that this has shed some light on the “mysteries” of chord shapes and which chords to use when playing in a particular key.