Chord Theory Chords Theory

Chord Theory 1: Basic Triads

Many guitar students know a few open chords and the ‘basic’ barre chord shapes, but get discouraged from furthering their chord vocabulary due to off-putting nomenclature (Gb7#9b13 anybody?) and immense (not to mention mostly useless) chord dictionaries with ‘10,000 Chords You Must Know’ – just where is the student supposed to start? And what is a ‘sus’ chord, an ‘augmented’ or a ‘diminished’ chord, anyway?

Know Your Intervals

Chords are built by stacking intervals on top of each other, so you’ll need to make sure you know your intervals first. You can find out all about them in my intervals lesson and even if you do know your intervals, it might be worth having that page open for reference – it has a big table which shows the number of semitones for any interval.

Stacking Thirds

Typically, chords are created by stacking thirds (either major or minor) on top of one another. For instance, in a C major chord, we have the notes C, E and G.

The interval from C to E is a major third (4 semitones), and the interval from E to G is a minor third (three semitones).

So the chord construction for a major triad is a major third on the bottom (C to E), and then a minor third on top (E to G).

As another example, the Cmaj9th chord has the thirds structure of major third, minor third, major third, minor third.

Chord Formulas

Another way of conceptualising the structure of chords is with a chord formula. A chord formula does not relate each note to its surrounding notes, but instead relates everything back to the root note. In the case of the Cmaj chord, the chord formula is 1, 3, 5. The number 1 refers to the root note (in this case C), the number three indicates a note a major third above the root which is E, and the number 5 indicates a note a perfect fifth above the root, which is G.

Here’s is the same principle of chord formulas, this time applied to the Cmaj9th chord. This gives us the maj9th chord formula which is 1, 3, 5, 7, 9.


Triads, as the name suggests, consist of three notes. Triads form the basis of western harmony, the most ‘basic’ (at least in terms of structure) are the major, minor, augmented and diminished triads.

Together these four chords cover every possible three note combination of stacked major and minor thirds, as shown in this table.

Chord TypeBottom ThirdTop Third
Major ChordMajor ThirdMinor Third
Minor ChordMinor ThirdMajor Third
Augmented ChordMajor ThirdMajor Third
Diminished ChordMinor ThirdMinor Third

Using this information, we can stack thirds to create the C major, C minor, C augmented and C diminished chords. We can then count up the semitones to arrive at the chord formulae.

The Major Chord Formula

The thirds structure of a major chord is a major third on the bottom and a minor third on top. Taking C as our root we find the next note by going up a a major third to the note E, and a minor third above the E to G. Therefore a C major chord uses the notes C, E, and G. C is the root and is marked as 1 (or R) in the chord formula; E is a major third above C which is marked as 3 in the chord formula; and G is a perfect fifth above C so it is marked as 5, which gives us the chord formula: 1, 3, 5 or R, 3, 5.

The Minor Chord Formula

From the table we know that a minor chord has a minor third on the bottom and a major third on top. Again, taking C as the root we find the next note by going up a a minor third to the note Eb, and a major third above that to G. Therefore a C minor chord uses the notes C, Eb, and G, where C is the root; Eb is a minor third above C and is written as b3 in the chord formula; and G is a perfect fifth above C so it is marked as 5. This gives us the minor chord formula which is: 1, b3, 5 or R, b3, 5. It is the minor third (b3) that gives the minor chord its name.

Augmented Chord Formula

Using the table to find the thirds structure we see that an augmented chord is built with two stacked major thirds. Starting on the note C we have the notes C, E, and G#. It is important that the last note is labelled G# not Ab. This is because, although G# and Ab are the same pitch, Ab is not a major third up from E – since E to A is four letter names, Ab would be a diminished fourth above E, not a major third above E.

The C is the root and marked 1 or R, the E is a major third from C and is marked 3; and the G# is an augmented fifth from C. This results in the augmented chord formula which is 1 3 #5 or R 3 #5. The augmented chord gets its name from the augmented fifth on the top of the chord (#5).

Diminished Chord Formula

Using the table, a diminished triad is two stacked minor thirds. Starting with C, Eb is a minor third up, and Gb is a minor third above that. So a C diminished chord contains C, Eb and Gb. Again, be careful that the top note is spelled Gb not F# since an F# is an augmented second above Eb not a minor third. Simple triads are always built in thirds.

So the chord formula for diminished chords will be 1 b3 b5. It is the diminished fifth on top (b5) which gives the diminished chord its name.

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