Joseph Haydn is often called the "father of the symphony," and there's a good reason for that. He played a very important role in shaping symphonies during the Classical period. Here's how he influenced this style of music:

1. Structure: Haydn created the four-part structure that we still use in symphonies today. This usually includes:

   • First movement: Fast and lively (Allegro) in a specific form called sonata form.
   • Second movement: A slow and beautiful piece.
   • Third movement: A dance-like piece called Minuet and Trio (which later changed to Scherzo).
   • Fourth movement: A lively piece called Rondo or another fast form.

2. Orchestration: He made the orchestra bigger and used more types of instruments. This made the music richer and allowed for new sounds. Haydn’s creative use of woodwinds, brass, and percussion inspired future composers.

3. Thematic Development: Haydn was great at taking simple musical ideas and changing them in interesting ways. He created variations and contrasts that kept listeners interested.

4. Humor and Surprise: One of his special traits is the fun surprises he included in his symphonies. He would have unexpected pauses or changes in volume. This made his music unpredictable and fun to listen to.

In conclusion, Haydn built a strong foundation for composers like Mozart and Beethoven. His inventive approach to the structure, the way he used instruments, and his unique expressions left a big mark on symphonic music.