system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do classical songs always have “in D minor, in E minor, in G major” what do those mean?
gpt
It’s because much of classical music is purely instrumental and has no lyrics and even, in a related way, no titles. After all, the titles of songs almost invariably come from the lyrics, directly or indirectly. So the names we use for many classical pieces are not really titles at all, only descriptions, and the musical key (e.g., “C major”), form (e.g., “sonata”) and tempo (e.g., “allegro”) are useful differentiators.  There are even numbering systems used, e.g., “K331” to address this same problem.