In his influential 1915 study on the historical development of the Viennese Classical style, Wilhelm Fischer claimed that one of the theme types of the Baroque, the Fortspinnungstypus, "turned into the sonata exposition" early in the Classical period. For Fischer, adding a subordinate theme within, or following, a core FS-type produced the Classical exposition. This paper assesses Fischer's claim by showing that sonata expositions of C.P.E. Bach were, in some cases, directly modeled on FS-type openings in works by his father J.S. Bach. A Haydn modeling on a movement from one of C.P.E. Bach's Württemberg sonatas shows the continued influence of the FS-type exposition.