Describe how to identify a Classical symphony and elaborate on a key musical form of the period.

The typical classical symphony can be identified through its use of standard forms and relatively simple methods of construction compared to later Romantic music.
Broadly speaking, a typical classical symphony would take the following form:1st movement - Allegro (or similar) in sonata form, sometimes with a slow introduction 2nd movement – Slow movement3rd movement - Minuet and Trio or Scherzo and trio - a dance movement with three beats in a bar - Beethoven famous altered the standard form by typically using a scherzo as opposed to a minuet (The well known 5th symphony offers a good example)4th movement – Allegro, also often in sonata form.
The eighteenth century featured a development of a form known as sonata form, consisting in its most simple form of three basic sections within the structure; the exposition, development and recapitulation. The form seems similar to ternary form in that it contains three sections, but actually stems from rounded binary form, which is an expansion of the simpler binary form prominent in music of the 17th and 18th centuries. Each of the three sections has its own purpose relating to harmonic and thematic structure. The aim of the exposition is to introduce the main thematic material, emphasising the tonal polarity of the tonic and dominant keys within the presentation of these subjects. The opening or first subject of the exposition appears firmly rooted in the tonic key, and the second (usually with contrasting melodic material) in the dominant key, offering contrasting musical statements which can be developed in the later sections, connected by a transitional passage. The transition section serves to destabilise the home key in order for the second subject to be introduced in the secondary key, so may move away from the tonic to undermine the tonal stability previously heard in the opening i.e. the first subject firmly in the home key. Following this is the development section, where the composers explores, elaborates and transforms the melodic material presented in the exposition, moving through different (but not always related) keys and often the subjects are fragmented and intertwined to develop and extend the original ideas. The final section is the recapitulation, which brings back the material from the exposition, re-establishing the home key, though the material may not be in exactly the same form as the opening and is usually modified; there is often variety in the returning section as well as a change in the function of the harmony, which in the case of the recapitulation is to return to the original key of the first subject.