We can make chords out of every note of the major scale by adding triads on to each note in the scale, using only the notes in that scale. For example, if we take the A major scale:
We know that the root note (A) becomes an A major chord when we add the 3rd (C#) and 5th (E) notes to it and play them simultaneously.
- If we take the 2nd note (B), and do the same thing, but this time using the B as a starting point, we will come up with the 2nd (B), 4th (D) and 6th (F#) notes as our triad (which is the 1st, 3rd and 5th notes relative to B). If we look at this triad closely, we find that it is a minor chord, since it contains a minor third (B to D = 3 semitones). So we get B minor.
- The 3rd chord (C#) will contain the 3rd (C#), 5th (E) and 7th (G#) notes of the scale. This triad also contains a minor third (C# to E) and so we get C# minor.
- The 4th chord (D) will contain the 4th (D), 6th (F#) and 1st (A) notes of the scale. This is a major triad, so we get D major.
- The 5th chord (E) will be composed of the 5th (E), 7th (G#), and 2nd (B) notes. This is a major triad, so we end up with E major. This is also the dominant chord in the key of A, so we can substitute E7.
- The 6th chord (F#) contains the 6th (F#), 1st (A), and 3rd (C#) notes. This is a minor triad, so we get F# minor. This is also the relative minor of A major.
- The 7th chord (G#) contains the 7th (G#), 2nd (B) and 4th (D) notes. This is a diminished triad, since both the 3rd and the 5th are flat, so we get G#minorb5.
These chords are the same across all major keys. So, in any major key, we will get the following chords:
The chord built on the 1st note of the scale is MAJOR
The chord built on the 2nd note of the scale is MINOR
The chord built on the 3rd note of the scale is MINOR
The chord built on the 4th note of the scale is MAJOR
The chord built on the 5th note of the scale is MAJOR (dominant)
The chord built on the 6th note of the scale is MINOR (relative minor)
The chord built on the 7th note of the scale is DIMINISHED (minorb5)
This is useful to know because it gives you a set of chords that are diatonic, or ‘in key’ since they only contain notes that are in the major scale of the key you are playing in. So you know that any of those chords will sound good together in that key. In fact, most popular songs which stay in a single key will almost exclusively use these chords from the key they are playing in.