See part 1
Dissonance in music is analogous to conflict in a story. Dissonance sounds “unpleasant” in the same way that conflict is unpleasant to the characters within the story, but then it would be an odd to have a story without any conflict. The opposite of dissonance is called consonance. Music commonly alternates between dissonance and consonance–creating tension, and then resolving it.
Conventional musical theory comes with a bunch of ideas about what’s consonant or dissonant. 400 cents, the major third, is considered consonant; 300 cents, the minor third, is considered dissonant. There’s some physical basis for these ideas, but arguably a lot of it has to do with tradition. 300 cents is more dissonant than 400 cents because that’s the meaning we’ve absorbed from our musical culture.
When you go outside the usual tuning system, musical tradition offers less guidance on what’s more or less dissonant. So this is the part of my intro to xenharmonic theory where I discuss a theory of dissonance that is independent of musical tradition.