The development of the classical style and its norms of composition formed the basis for much of the music theory of the 19th and 20th centuries. As an overarching formal principle, sonata was accorded the same central status as Baroque fugue; generations of composers, instrumentalists, and audiences were guided by this understanding of sonata as an enduring and dominant principle in Western music. The sonata idea begins before the term had taken on its present importance, along with the evolution of the Classical period's changing norms. The reasons for these changes, and how they relate to the evolving sense of a new formal order in music, is a matter to which research is devoted. Some common factors which were pointed to include: the shift of focus from vocal music to instrumental music; changes in performance practice, including the loss of the continuo .