I’ve been trying to learn about functional harmony and I keep asking myself the above question. Each chord seems to have a general function (with exceptions) within scales, but why is that so? Were scales made with those functions in mind, or were those functions agreed upon or discovered after scales were already determined? Is it a result of having 7 notes in a scale? For example, if you were to choose 7 random notes within an octave...would the 5th chord always serve a dominant function?
DISCLAIMER: I know I’m asking a simple question that doesn’t have a simple answer and I don’t expect any response to be cut and dry. I also realize I’m making a lot of assumptions about the way music works that may or may not be true, however any insight at all would be helpful! Thanks!