Primary Triads & Writing a Melody
The three most useful chords in any key, and how to use them to support a melody of your own.
Explainer
The primary triads are the three most useful chords in any key — built on scale degrees 1, 4 and 5: the tonic, subdominant and dominant. Together they can harmonise almost any simple melody.
In C major: I (tonic) is C-E-G, IV (subdominant) is F-A-C, V (dominant) is G-B-D.
When writing a melody of your own, look at the shape so far and the key it's in — usually the strongest ending is a step or short leap onto the tonic, often supported underneath by a V-to-I chord change.
Always check your finished melody by playing or singing it back — your ear catches what the eye on the page misses.
Worked examples
The tonic triad (I)
C, E and G in C major — the "home" chord.
The subdominant triad (IV)
F, A and C in C major — a strong step away from home.
The dominant triad (V)
G, B and D in C major — creates tension that pulls back to the tonic.