Passing chords

You know those short chords that, though not part of the main chord progression, help you pass from one chord to the next?

Those are passing chords: extra points of harmonic detail that shore up the tune’s structure. Generally played quite briefly, they work like stepping stones between the main chords in a progression, providing harmonic enrichment and variety to spice up otherwise humdrum passages.

Passing chords needn’t be in the same key you’re playing in, in fact they mostly work better if they’re from another key. When using them, it’s good to look at things from the view of where your progression is going, rather than the chord