Suppose you're playing a melody and your ear tells you that the chord needs to be changed. Why? And then you go ahead and try every chord in that key until one of them sounds right. Great. But why does it?
Normally, the chord changes when an emphasized note (is there an official term for it?) does not "speak to" the chord you're playing. What makes a note "speak to" the chord?
Sometimes this note is the first note of the three-note chord. Other times, it's the last note of the three-note chord. And then there are times when this note isn't part of the three-note chord at all, and yet your ear tells you that it "fits" (or not: I'm always confused by this - how do you pluck out a chord that does not contain the note you're playing).
Why? Is there a technical explanation for it?
For instance, while most popular songs have three or four chords, Don McLean's American Pie has a ton. What is so different about McLean's melody?
The opening of Vissi d'arte goes like this:
Note that it's in D-minor. Note also that the final two notes of the second phrase, "viva!" are the same pitch: it's an E.
The chord there is A (major). Which is the dominant. It is said that the dominant leans towards the tonic and wants to be resolved.
Does this mean that if, playing in D-minor, you end a phrase in E, the chord would ALWAYS, INVARIABLY be A? And not, say, A7, or Em, for that matter?