i'm referring to a major chord: C-E-G with an added ninth D.
is this considered a stable chord?
the melody usually is on that ninth (D), but ..how does it get away with it? that should be tension.
i've heard this taylor swift - style which has the chorus on the added ninth. normally that would be a major second (to the harmony), which is an unusual tone to start a *concluding melody* like a chorus, but it would be somewhat acceptable if it would resolve to the root. but here it "resolves" to the fifth, like a half cadence. finally it rests on the second/ninth as a conclusion (the second/ninth sounds more stable than the fifth)
so what's with this added ninth, not just as chord embellishment, but as the central tone in the melody line?