Hearing the chord under the tune · From Zero to Mozart

The capstone of the harmony movement, and the ear half of reading-a-chord-chart: play a plain tune and hear, bar by bar, which chord is under it — even though no chord is sounding. This is what lets you harmonise a melody, join a jam, or write the chart yourself.

Most bars sit on one chord

In simple tunes the harmony changes slowly — often once a bar, sometimes once every two. And the melody notes in that bar are mostly chord tones of whatever chord it is. So:

Which notes does this bar dwell on? The long notes, the downbeats, the first and last notes.
What chord contains those? Usually I, IV or V of the key.
Check it against the three functions (home-leaving-pulling) — does a resting chord fit here, or a pulling one?

66 bpm

Play the melody (no chords). Bar 1 dwells on G and B — both notes of a G chord (I). Bar 2 on C and E — a C chord (IV). Bar 3 on A and D, and it feels like it's pulling — a D chord (V). Bar 4 home — G (I). Reveal shows the chart; hear it before you look.

Try it

Try

Take Twinkle in G (you numbered it in degrees-in-your-tunes). Sing the first line and, for each bar, try a G chord and a D chord underneath in your head — one will fit and one will clash. Bar 1 (^1 ^1 ^5 ^5) wants G; the "^6 ^6 ^5" bar wants D (or G, depending on the version); the descent ^4 ^3 ^2 ^1 lands back on G. Write your guessed chart, then play the melody with a friend or a drone and hear if it holds.

The usual mistake

Trying to name the chord from a single note. One melody note usually fits two or three chords — B in G major is in G (as ^3), in E minor (as ^5), in a D chord... only later. Use the whole bar, weight the long notes, and lean on function. The other mistake: expecting the chord to change on every note. In most simple tunes it's one chord per bar or slower — harmonic rhythm (Stage 4 harmonic-rhythm) is usually slow.