In Schubert's instrumental music there is to be observed a phenomenon best described as his ‘volcanic temper’ since it bears a striking resemblance to the two natural phenomena of volcanic eruption and of choleric temper. It represents a side of his art remote from the familiar lyrical Schubert, and although the passages where this darker side turns its face are generally well known, its character and significance are often mistaken in performance and criticism. There is a streak of violence and distemper in the music that makes itself felt in the most unmistakable ways. Some examples must be offered.

First, to choose one of the most familiar, the slow movement of the Octet, D. 803. In the coda the first violin begins a solo statement of the melody, followed canonically two bars later by the second violin and two further bars later by the viola. A quiet playing-out of this theme is expected as a close to a long tranquil movement, but instead there is an extraordinary and unpredictable gathering of tension. The viola entry becomes a two-bar crescendo on a descending diminished seventh and arrives with horrifying suddenness on a violent sforzando and a colossal explosive pizzicato on cello and double bass (see ex. 2.1). One bar later the diminished seventh has resolved on to a plain dominant seventh and the dynamic is piano as though nothing untoward had happened.