How did Schumann and Mendelssohn remain closer to Classical symphonic forms than Berlioz and Liszt?

In the context of the symphony, Robert Schumann and Felix Mendelssohn maintained a closer adherence to Classical symphonic forms than Hector Berlioz and Franz Liszt by departing less widely from established norms and placing less emphasis on extramusical associations.1

While all four composers were deeply concerned with formal discipline, Berlioz and Liszt represented a trend toward greater freedom and the integration of extramusical content, such as literary programs or legends. Their works often utilized thematic transformation—where a theme is modified to suit a dramatic or programmatic narrative—rather than the traditional motivic development characteristic of the Classical sonata form.123

In contrast, Schumann and Mendelssohn remained more conservative in their approach. Their compositions generally followed the patterns of their Classical predecessors, such as Joseph Haydn and Wolfgang Amadeus Mozart, and they avoided the explicit programmatic structures that defined the works of Berlioz and Liszt. Although Schumann experimented with fusing movements together, he and Mendelssohn remained more aligned with the structural rigour and abstract musical goals of the Classical tradition.132