Diatonic Chord Function
Now that we know how to build various types of chords and triads, we will look at how these
triads function within a given key.
This is easiest to understand by looking at the key of C major. In the key of C major there
seven notes with no sharps and no flats – C D E F G A B (with the next note being C again).
Finding the “Diatonic Chords” of a particular key simply means finding the chords or triads
that can be made using the notes from that key and only the notes from that key.
To do this, you must take each of the seven notes of the key and build a triad. Here are the
seven possible triads for C major.
(Remember that Triads are build by stacking the interval of a 3rd on top of a note and then
stacking the interval of a 3rd on that. For example, a 3rd above C is E and a 3rd above E is G.
Thus, for the triad based on the note C, we get the notes C-E-G)
When we examine the chord quality (whether a chord is major or minor, etc) of the Diatonic
Chords for C major we find the following.....
C-E-G = C MAJOR
D-F-A = D Minor
E-G-B = E minor
F-A-C = F MAJOR
G-B-D = G MAJOR
A-C-E = A Minor
B-D-F = B diminished
(Remember that determining whether a triad is Major or Minor depends on the interval
relationship between the notes of the triad. Major = M3 + m3. Minor = m3 +M3)
This formula of major and minor triads can be applied to any key by replacing the note names
with Roman Numerals that represent degrees of a major scale. For example, C would
become one, D would become two, E would become three, etc. (Traditionally, Major triads
are represented with Capital Numerals, while minor triads are represented by lower case
C D E F G A B C
MAJ min min MAJ MAJ min dim MAJ
I ii iii IV V iv vii I