Symphony No.100 in G major, Hob. I:100 "Military Symphony"

The first movement is in sonata form with a slow introduction that hints at motifs that will appear later in the movement. The Allegro begins with a dancing theme which is unexpectedly scored only for flutes and oboes. The strings respond by repeating the theme an octave lower. The tutti then transitions the music to the dominant key for the second subject area, which begins with the first theme transposed to D major. This theme is briefly developed in D minor before a new subject in the dominant is stated with a rocking motif in the violins. Haydn's use of themes and keys here demonstrates an important point about sonata form: the second subject is defined by the new key , not (only) a new theme. The repetition of the 1st subject in the dominant in this movement, at bar 75, is therefore the beginning of the 2nd subject area, even though the new theme does not appear until some twenty bars later.