Full Idea
The 'expression theory' holds that if music is sad that is because it expresses the composer's sadness, ...but composers take a long time composing sad works, and may even been gleeful at receiving payment for it.
Gist of Idea
It seems unlikely that sad music expresses a composer's sadness; it takes ages to write
Source
Stephen Davies (The Philosophy of Art (2nd ed) [2016], 6.4)
Book Reference
Davies,Stephen: 'The Philosophy of Art (2nd ed)' [Wiley Blackwell 2016], p.143
A Reaction
[compressed] Pretty conclusive. I see composing as like acting. Just as you can put on a happy or sad face, so a composer can discover music that feels sad or happy. Three movement sonatas don't fit expression at all.
Related Ideas
Idea 20404 Music isn't just sad because it makes the listener feel sad [Davies,S]
Idea 20405 Music may be expressive by being 'associated' with other emotional words or events [Davies,S]