Fewer and fewer oratorios and cellars were composed in the classical period, but the biggest difference was the subject of the work. Baroque works were based on classical mythology but in the classical era they transformed into a more realistic contemporary subject that reflected the ideas of the Enlightenment present in the classical era. Some of the main differences between the works of these two eras, however, were subject matter and form. In the Baroque era, serious opera was very common. Serious opera was characterized by its rigid form and its appeal to authority or those in power. Later Baroque opera emphasized strophic variation over the da capo aria established as a vocal form. Along with these forms was the bipartite aria, which consisted only of variations A and B. In contrast to late Baroque opera and its rigid alternation of recitative and aria, mid-Baroque opera retained great formal flexibility. opera was introduced. This change may be somewhat contributed to Cristoph