The most famous of musical forms also happens to be one of the most difficult to fathom.

I’ve heard them a thousand times, but what actually is a symphony?
In its loosest form, a symphony is an extended work for orchestra. E.T.A. Hoffmann described it as an “opera of instruments”. The word comes from the Greek syn (together) and phone (sounding). Symphonies are generally structured into several movements. If you take the strictest definition, a symphony must contain at least one movement in sonata form.

What is sonata form anyway?
Your standard sonata consists of three parts: an exposition, in which the themes, or melodies, of the piece are stated; a development section which explores and expands on these motifs and introduces new ideas through varying instrumentation and harmonic progression; then a recapitulation, in which the original themes of the exposition are repeated in a new light. Sonata form also allows for an introduction, to ease the listener into the symphony or start with a catchy theme that would be too light for the exposition (as in Haydn’s Drumroll Symphony No 103), and a coda, usually a brief tailpiece to finish the movement.

How many movements should a symphony have?
From the height of the...