The definition of sonata form in terms of musical elements sits uneasily between two historical eras. Although the late 18th century witnessed the most exemplary achievements in the form, above all from Joseph Haydn and Wolfgang Amadeus Mozart, a compositional theory of the time did not use the term "sonata form". Perhaps the most extensive contemporary description of the sonata-form type of movement may have been given by the theorist in 1793: like earlier German theorists and unlike many of the descriptions of the form we are used to today, he defined it in terms of the movement's plan of modulation and principal cadences, without saying a great deal about the treatment of themes. Seen in this way, sonata form was closest to binary form, out of which it probably developed.