What is Sonata form?

Sonata form is a way of structuring a piece of music, which was first used in the 18th century by Beethoven. After Beethoven, lots of future composers adopted the structure as the first movement of their symphonies.  Sonata form is similar to ternary form (ABA - like a sandwich with bread-filling-bread) in the way that it contains three main sections. These sections are called: EXPOSITION - where the main ideas of the piece of music are introduced for the first time. DEVELOPMENT - these ideas are then explored further, often with modulations (key changes - so the main ideas can go from being major (happy) to minor (sad). RECAPITULATION - the ideas are heard one final time but are their original form.