Upon very careful revision of this explanation, and reference to the given diagrams, the student will perceive that the distinctive trait of the sonata-allegro form is the section of Development which it contains; and that of the three Rondo-forms is the absence of such a Development.

Of the mixed forms under consideration there are two: one in which a section of _Development_ is introduced into the Rondo (as substitute for one of its Subordinate themes); and the other a sonata-allegro, in which the Development is omitted, and a new theme (a sort of additional Subordinate theme) inserted in its place.

In other words, a Rondo (second or third form--probably _not_ the first rondo-form) with a Development; and a sonata-allegro with a new Middle theme, or Episode (as we have already called it).
The Rondo with Development is illustrated in Beethoven, pianoforte sonata, op.

27, No.

1, last movement; it is the third rondo-form, designed as follows:-- _Principal Theme_, Two-Part form (measures 1-24).
_Transition_ (25-35).
_First Subordinate Theme_, period, extended,--or phrase-group (36-56).
_Codetta_ (57-72).
_Re-transition_ (73-81).
_Principal Theme_ (82-97).
_Transition_ (98-106).