What do these two keys already share?

Answer

Understand

Two keys close together on the circle of fifths share most of their diatonic pitches; two keys far apart share very few. A shared pitch alone is a starting point, but a shared chord, one whose root and quality are diatonic in both keys, is a stronger bridge, since it can function coherently in either key at the moment of the pivot.

Worked examples

C major and G major, one fifth apart, share C, D, E, G, A, and B, six of their seven notes. C major to A major, three fifths apart, exposes noticeably fewer shared notes, since the two keys' own accidentals diverge much more the further apart they sit on the circle of fifths.

Method and limitations

The tool builds each key's own diatonic degree table, intersects their pitch-class sets for the shared-tone list, then checks every shared pitch for a chord quality diatonic in both keys at that root, retaining each key's own numeral label so the bridge reads correctly from either direction. This tool does not attempt every possible chromatic pivot chord, only ones built on genuinely shared diatonic pitches, and it never claims a theoretically valid bridge will sound smooth or convincing in an actual piece.

This tool is deliberately narrower than Modulation Planner, which compares every viable route between two keys regardless of shared material; here, only pivots built on tones or chords both keys already hold in common are surfaced, since that shared-tone evidence is specifically what makes a modulation feel prepared rather than abrupt. A destination key with very few shared pitches is not unreachable, it simply needs a different kind of pivot this narrower tool does not search for.

Next decisions

• First, understandKey Signature Explorer
• Compare another routeModulation Planner