What is sonata form structure, and how is it used by Beethoven in the first movement of the 'Pathetique'?

Sonata form could be described as a larger, more complicated ternary (ABA) form. It has three sections - the exposition, the development and the recapitulation. In the exposition there are two main musical ideas (the first subject and the second subject). These musical ideas are broken down and explored in the development, and brought back in the recapitulation. Beethoven's sonata form is unusual as he includes a slow introduction before the exposition starts. The musical ideas from this introduction can also be heard at the start of the development section, as well as in the movement's coda. This movement is also unusual as Beethoven chooses to put the second subject in the recapitulation in F minor (the subdominant) rather than C minor (the tonic) as would be more traditional.