Reharmonization · Music theory
Changing the chords of a melody while keeping the melody: what can be changed, with what tools, and a complete step-by-step example.
The melody stays
To reharmonize is to put other chords under the same melody. It is the central tool of arranging: a well-known tune can sound new without changing a single note. And there is only one firm criterion: each melody note must be a chord note, an available tension or a well-placed passing note.
There is no correct result. An arrangement is judged by its effect, not its rules, and keeping some of the original harmony often works better than changing everything: what surrounds the new color matters too. What you have learned so far is a toolbox, not a recipe.