Final answer:
Nineteenth-century symphonies retained the overall structure of the Classical symphony but often diverged from Classical rules, with Romantic-era composers pushing musical boundaries and embracing nationalistic themes and innovative musical techniques.
Step-by-step explanation:
Even though nineteenth-century symphonic compositions retained the basic structure of the earlier Classical symphony, they did not always follow the "Classical rules". Despite this, Romantic era composers did not completely reject Classical music. They emulated great classicists like Haydn, Mozart, and Beethoven and maintained the key rules for forms, rhythm, melody, harmony, harmonic progression, tuning, and performance practice from the Classical period. Innovations were made in instrument construction during the Industrial Revolution, leading to increased use and complexity of wind instruments in orchestral settings. Some composers, like Arnold Schoenberg, pushed boundaries even further by experimenting with atonality and creating new musical scales, challenging Western music traditions.
During the post-Romantic era, many composers focused on nationalistic themes or extended Romantic techniques to their limits. This era included the final decades of the nineteenth century and the first decades of the twentieth century. It was a time of great experimentation and shifting towards new music styles like Impressionism and Modernism, which continued into the twentieth century. The socioeconomic shift with the rise of the middle class also impacted the audience for music, broadening from aristocratic patrons to the general public in large concerts and festivals.