What characteristic defines 'classical' music?

The defining characteristic of 'classical' music is its use of structured forms and established conventions. This genre of music is characterized by specific formats and guidelines that dictate how compositions are arranged and performed. These structures can include forms like sonata, symphony, concerto, and opera, each with its own set of rules regarding structure, development, and thematic presentation.

Classical music often adheres to certain aesthetic ideals and conventions that aim for balance, clarity, and emotional depth. Composers like Mozart, Beethoven, and Bach utilized these conventions to create music that has stood the test of time, showcasing not only technical skill but also profound expression.

The other options point to characteristics that are generally more prominent in other genres of music. For example, improvisation is a significant aspect of jazz and some folk traditions, while contemporary themes might be more applicable to modern genres, including pop and hip-hop, which focus on current events or trends. The usage of only acoustic instruments is also misleading, as classical music has incorporated various instruments, including those in the orchestra, which may feature both acoustic and electronic elements in certain modern compositions. However, the core of classical music firmly rests on its structured forms and established conventions, making that aspect the most defining characteristic of the