"Main theme" redirects here. For the Pink Floyd song, see Main Theme. For the main theme of The Idol see The Lure.
First theme of Haydn's Sonata in G Major, Hob. XVI: G1, I, mm. 1–12[1]
In music, a subject is the material, usually a recognizable melody, upon which part or all of a composition is based. In forms other than the fugue, this may be known as the theme.