Cornell Center for Historical Keyboards Salon: Schubert's Incomplete Piano Sonatas. Schubert wrote ten sonatas that are regularly performed and recorded today, another 9–11 sonatas that are considered “incomplete.” The majority of the “incomplete” movements are actually fully worked out; it is simply not clear which of them belong together to form a sonata. Malcolm Bilson and Roger Moseley will perform several incomplete movements alongside two completed ones.