Music theory provides musicians with some basic forms. The sonata was the most popular form used by instrumental composers from the mid‐18th century until the beginning of the 20th century. This form is considered by many to be the first true break from the liturgical music that had made such an impact on Western music from the Medieval period on through the Baroque period.
Sonatas are based on the song (ternary) form, ABA, which means they have three defined parts: exposition, development, and recapitulation. The true genius of the sonata is that not only does its structure allow many of the rules of basic music theory to be broken, but it also encourages such defiance. With a sonata, it’s perfectly allowable to switch to a new key and time signature in the middle of the song.
Starting with the exposition
The first part of a sonata, called the exposition, presents the basic thematic material of the movement, or each self‐contained part of a piece of music. This part is also often broken up into two thematic parts:
First part: Generally, the first part of the exposition presents the main theme of the song, or the musical “thread” that ties the piece together. This first part usually is the line that sticks the most in your head.
Second part: The second part of the exposition is a “reflection” of the first part, in that it sounds a lot like the first part but is slightly changed.
Put on Beethoven’s Sonata in C Minor, Opus 13 to get a good example of these two defined parts.
Moving on to something new: Development
The second part of the sonata form, called the development, often sounds like it belongs to a completely different piece of music altogether. In this part, you can move through different key signatures and explore musical ideas that are completely different from the original theme.
Often this part of the sonata is the most exciting. Here you can include your big chords and increase tension with the use of stronger rhythm and greater interval content (number of interval steps between each note).
Check out this excerpt from the development of Sonata in C Minor, Opus 13.
Taking a rest with recapitulation
After the excitement of a sonata’s development, it feels natural to come to rest where you began. The third and final part of a sonata is the recapitulation, where the composition returns to the original key and the musical theme expressed in the first section and brings it all to a close. Here’s an excerpt of the final movement of Beethoven’s Sonata No. 8. Sonata in C Minor, Opus 13.