Editing Three-key exposition

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.

==Examples== 

* A very early example appears in the first movement of [[Joseph Haydn|Haydn]]'s String Quartet in D major, Op. 17 No. 6: the three keys are D major, C major, and A major. (C major is prepared by a modulation to its relative minor A minor, which happens to be the dominant minor of the original key.)
* [[Ludwig van Beethoven]] wrote a number of sonata movements during the earlier part of his career with three-key expositions.  For the "third" (that is, the intermediate) key, Beethoven made various choices:  the dominant minor ([[Piano Sonata No. 2 (Beethoven)|Piano Sonata No. 2, Op. 2 no. 2]]; [[String Quartet No. 5 (Beethoven)|String Quartet No. 5, Op. 18 no. 5]]), the [[supertonic]] minor ([[Piano Sonata No. 3 (Beethoven)|Piano Sonata No. 3, Op. 2 no. 3]]), and the relative minor ([[Piano Sonata No. 7 (Beethoven)|Piano Sonata No. 7, Op. 10 no. 3]]). Later, Beethoven used the supertonic major ([[Piano Sonata No. 9 (Beethoven)|Piano Sonata No. 9, Op. 14 no. 1]], [[Piano Sonata No. 11 (Beethoven)|Piano Sonata No. 11, Op. 22]]), which is only a mild sort of three-key exposition, since the supertonic major is the dominant of the dominant, and commonly arises in any event as part of the modulation. As he entered his so-called "middle period," Beethoven abandoned the three-key exposition.  This was part of a general change in the composer's work in which he moved closer to the older practice of [[Joseph Haydn|Haydn]], writing less discursive and more closely organized sonata movements. 
* [[Franz Schubert]], who liked discursive forms for the entirety of his short career, also employed the three-key expositions in many of his sonata movements. A famous example is the first movement of the [[Death and the Maiden Quartet]] in D minor, in which the exposition moves to F major and then A minor (translated to D major and minor respectively in the recapitulation), a formula that is repeated in the final movement; another is the Violin Sonata in A major (in which the second theme appears in G major and B major, while only the closing passage of the exposition is in the dominant, E major). His [[Piano Sonata in B major D. 575 (Schubert)|B major piano sonata]], D 575, even uses a four-key exposition (B major, G major, E major, F-sharp major): this key scheme is literally transposed up a fourth for the recapitulation. The finale of his [[Symphony No. 6 (Schubert)|sixth symphony]] (D 589) is an even more extreme case: its exposition passes from C major to G major by way of A-flat major, F major, A major, and E-flat major, making a six-key exposition.
* [[Felix Mendelssohn]] followed the Death and the Maiden example in the first movement of his second Piano Trio, in which the E flat major second theme gives way to a G minor close (transposed to C major and minor in the recapitulation). 
* The first movement of [[Frédéric Chopin]]'s [[Piano Concerto No. 2 (Chopin)|Piano Concerto in F minor]] also has a three-key exposition (F minor, A-flat major, C minor).
* The first movement of the [[Cello Sonata No. 2 (Brahms)|second cello sonata]] by [[Johannes Brahms|Brahms]] also employs a three-key exposition moving to C major and then A minor, the exposition of the first movement of the [[String Sextet No. 1 (Brahms)|String Sextet in B flat]] involves an intervening theme in A major before reaching F, and the [[Piano Quartet No. 1 (Brahms)|Piano Quartet in G minor]] involves secondary themes in D minor and major respectively (the first of these being omitted in the recapitulation and the second transposed to E flat major moving back to G minor). The [[Violin Sonata No. 3 (Brahms)|D minor violin sonata]] has a final movement that moves through a calm second theme in C major before closing the exposition in A minor.

== Further reading ==

*Longyear, Rey M., and Kate R. Covington (1988). Sources of the three-key exposition. ''The Journal of Musicology'' 6(4), pp. 448-470.
*[[Charles Rosen|Rosen, Charles]] (1985) ''Sonata Forms''.  New York: Norton.
*Graham G. Hunt; When Structure and Design Collide: The Three-Key Exposition Revisited, Music Theory Spectrum, Volume 36, Issue 2, 1 December 2014, Pages 247–269.

[[Category:Formal sections in music analysis]]