Listen to recordings of music, which is the best way to compare composers. Often you can borrow CDs at the local library, and there is a wide selection of recordings on the Internet. Sometimes classical music can be downloaded for free.
Select works from Mozart and Beethoven. Mozart's body of work contains over 600 compositions; Beethoven, around 300 compositions. It is important to select music written for a certain instrument, such as the violin, or a form or genre of music, such as a concerto or sonata. A good start is Mozart's 40th Symphony and Beethoven's Fifth. Beethoven adapted a sequence from Mozart's 40th Symphony into his own Beethoven's Fifth. Beethoven's own sketchbook contains evidence of the sequence that he adapted.
Listen to the music that you have chosen and try to identify similarities and differences in style. Mozart was a composer in the Classical Era, while Beethoven was one of the earlier composers working in the Romantic Era. Beethoven is also classified as belonging to the late Classical Era.
Look at the keys the composers used and identify the moods that the composers are evoking. Mozart wrote his 40th Symphony under difficult circumstances. His growing poverty and fading popularity as well as increasing marital strains resulted in "black thoughts," according to a letter Mozart wrote to his friend Michael Puchberg. Beethoven's Fifth is also a dark piece.
Select an earlier symphony of Mozart and compare it to Beethoven's Fifth. Mozart's music is often cheerful, while Beethoven's music is darker and deeper.