Chord Names: a wee bit of theory, part 1

The basics make a lot more sense if you understand just a small amount of the theory that lies behind how chords are made: from triads, 7ths and extensions.

The basic harmonic building block is the triad. Take any scale, pick a note. That note is note 1, count up the scale until you get to note 3, then count again until you get to note 5. Those three notes, every other note in the scale, form a triad, and basic chords are all derived from triads.

So, the C major scale is: C D E F G A B

If we count 1, 3 and 5 from C, we get C E G. Those three notes form a C major triad. Major because the interval between C and E is a major 3rd (or 4 semitones, or 4 frets on the guitar neck). You might play it:

What happens if we count from a note other than the first note in the scale? In the C major scale if we count from D we get D F A. This is a minor triad because the interval between D and F is a minor 3rd (or 3 semitones, or 3 frets on the guitar neck).

The interval between the 1st and 3rd defines whether a triad (or the chord built on that triad) is a major or minor chord. There’s nothing more to the major/minor distinction than that.

What about the interval between 1 and 5? If the interval is a perfect 5th (7 semitones or 7 frets on the guitar neck) then the triad is just a major or minor triad, depending on the first two notes.

However, if the interval is one semitone (or one fret) less than a perfect 5th, the 5th is said to be diminished and the combination of a minor 3rd and a diminished or b5 is a diminished triad. If the interval is one semitone (or one fret) more than the perfect 5th, the 5th is said to be augmented and the combination of a major 3rd and an augmented 5th or #5 is an augmented triad.

If we count from B in the C major scale above, we get B D F. A minor 3rd and a diminished or b5. So a triad built on B in the key of C is a diminished triad.

You can’t get an augmented triad from a major scale. There’s no note in the scale where counting from that note will give you the combination of a major 3rd and a b5.

As an example, though, you could play one like:

Since basic jazz and popular song harmony is based around the harmonies built on the major scale the three key ‘flavours’ of triad are major, minor and diminished and all the standard chords, no matter how many extra notes are stacked on top, retain a major, minor or diminished tonal quality.

To recap:

major triad – major 3rd + perfect 5th: 1 3 5

minor triad – minor 3rd + perfect 5th: 1 b3 5

diminished triad – minor 3rd + diminished 5th: 1 b3 b5

augmented triad – major 3rd + augmented 5th: 1 3 #5

In the next part, I’ll look just at simple major chords — those that contain nothing but the 3 notes from the major triad — and look at fingerings, inversions and ‘swing’ voicings.

~ by Matt on June 21, 2008.