How did Felix Mendelssohn combine Classical musical forms with Romantic ideas?

Felix Mendelssohn is celebrated for his ability to bridge the gap between the Classical and Romantic eras by grounding his work in traditional models while infusing it with new expressive qualities.1

He combined these styles through the following approaches:

• Adherence to Classical Models: Mendelssohn largely observed the practices and structures established by his Classical predecessors, such as Wolfgang Amadeus Mozart and Ludwig van Beethoven. His compositions, including his sonatas, generally followed the established patterns of these earlier masters.12
• Romantic Expression: He initiated key aspects of Romanticism, an artistic movement that prioritized feeling and imagination over rigid tradition. His music is noted for its poetic nature, fresh lyrical melodies, and atmospheric effects, which are particularly evident in works like the Overture to A Midsummer Night’s Dream and the Scottish Symphony.13
• Innovation within Form: While he maintained traditional structures, he introduced original elements such as the "swift-moving scherzo," a playful movement that became a hallmark of his style.43