system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do major and minor keys in music convey different emotions?

Are major and minor keys interpreted differently because they actually for some reason evoke those emotions, or has the association of keys with emotions in media help dictate which is 'happy' and which is 'sad'?
gpt
There is no strict rule saying that major or minor keys are for happiness and sadness, respectively.

However, a minor third is slightly more "dissonant" than a major third. In general, dissonance is less pleasing to the human ear, and won't induce a complete, resolved, happy emotion.

Diminished triads sound particularly frightening and sad. This is because more dissonance is involved with a diminished triad (two minor thirds, one stacked on top of the other)