Sonata form is a musical structure that became popular in the Classical period, consisting of three main sections - the Exposition, Development, and Recapitulation. In the Exposition, the main themes are introduced, including the rhythmic first subject and more lyrical second subject, which is usually in a related key. The Development section transforms fragments of the themes, and the Recapitulation restates the Exposition with the second subject now in the tonic key. Tchaikovsky's Romeo and Juliet Fantasy Overture employs sonata form and features themes representing strife, love, and Friar Lawrence.