Original sentence: Accordingly there is a large body of theory on what unifies and distinguishes practice in the sonata form, both within eras, and between eras.Even works which do not adhere to the standard description of a sonata form often present analogous structures, or are meant to be elaborations or expansions on the standard description.Study of the sonata form in music theory rests on a standard definition, and a series of hypotheses about the underlying reasons for the durability and variety of the form.The sonata form, since its establishment, became the most common form in the first movement of works entitled  "sonata", as well as other long works of classical music, including symphonies, string quartets and tone poems.The standard definition focuses on the thematic and harmonic organization of tonal materials, which are presented in an exposition, elaborated and contrasted in a  development and then resolved harmonically and thematically in a recapitulation
Edited sentence: Accordingly there is a large body of theory on what unifies and distinguishes practice in the sonata form, both within eras and between eras.Even works which do not adhere to the standard description of a sonata form often present analogous structures or are meant to be elaborations or expansions on the standard description.Since its establishment, the sonata form became the most common form in the first movement of works entitled  "sonatas", as well as other long works of classical music, including symphonies, string quartets and tone poems.Study of the sonata form in music theory rests on a standard definition and a series of hypotheses about the underlying reasons for the durability and variety of the form.The standard definition focuses on the thematic and harmonic organization of tonal materials which are presented in an exposition, elaborated and contrasted in a  development and then resolved harmonically and thematically in a recapitulation