50. Diatonic Harmony Review 1

When we build 3 note chords from each note in the major scale, we say we have harmonized the major scale.  We see that there are seven chords made from it, one for each scale degree. The chords built from the 1st, 4th and 5th degrees of the scale are MAJOR chords (I, IV, V). These are called the primary chords of the scale.


These three chords are the basis of the vast majority of popular music; indeed there are thousands of songs written with only them. The other four chords from the scale are called secondary chords. Three of those four chords—the ones built on the 2nd, 3rd and 6th degree, are MINOR chords.


The other chord, the one built on the 7th degree, is a DIMINISHED chord. Although diminished chords are important in some music, and its construction is outlined in the Triad Types page (Appendix 1), its function in diatonic harmony is very similar to the V chord, so much so that we will disregard it for now. Let’s concentrate on the other six. Remember:


I, IV, and V are MAJOR chords, in EVERY key.

ii, iii and vi are  MINOR chords, in EVERY key.


Again, when chords are arranged in some order, it is a progression. Usually a song begins on the tonic chord (I) from a particular scale. Typically the song will then use other chords diatonic to that scale, moving to them and back to I again. Thus the scale of the tonic chord is said to be the key.  All the diatonic chords from that scale are said to be in its key.


In the key of C, this means C major, D minor, E minor, F major, G major, A minor, and B diminished. In written music, the key is notated by a key signature, an instruction at the beginning of a piece indicating its key. The diatonic chords in the five keys most used by guitarists are C, A, G, E and D. They spell the word CAGED as an acronym, but also recognize that these keys are the following:

C, which has no sharps or flats…

and the keys that contain 1,2,3 and 4 sharps–G, D, A and E, in that order. (See the reference page Sharps in Order in Appendix 1)

The circle of fifths is a teaching tool that helps with this. It shows that the number of sharps increases by one as you move in 5ths clockwise around the circle. (See 39. The Circle of Fifths for more on this)

© 2012 Jim Greenfield