Editing Three-key exposition (section)

In music, the '''three-key exposition''' is a particular kind of exposition used in [[sonata form]].

Normally, a sonata form exposition has two main key areas.  The first asserts the primary key of the piece, that is, the tonic.  The second section moves to a different key, establishes that key firmly, arriving ultimately at a cadence in that key.  For the second key, composers normally chose the [[dominant (music)|dominant]] for major-key sonatas, and the [[relative major]] (or less commonly, the minor-mode dominant) for minor-key sonatas.  The three-key exposition moves not directly to the dominant or relative major, but indirectly via a third key; hence the name.