I have decided to make a change in terminology, which I will use from this point forward. I will also try to update previous posts as quickly as I can.
I have recently been using the term "major dominant ninth chord," but I admit that's caused confusion and so I am reverting to "dominant major-ninth chord," which fits better with the common label "dominant ninth chord." Here that is in Mark DeVoto's chapter on Debussy: "The dominant major ninth sonority D♭–F–A♭–C♭–E♭." ("The Debussy sound: color, texture, gesture," in The Cambridge Companion to Debussy, 189.)
No matter what labels and terms one uses, there is some kind of awkwardness and one has to rely on whatever convention is being observed. Under (a) below is C7, but note that it is not diatonic in C major--that's G9--but it can be called a "dominant seventh chord" anyway. Likewise with C9 under (b). Thus, "dominant ninth chord" becomes a general category, regardless of how the chord is actually used in any musical context. The even more general "ninth chord" is used by some authors, especially more traditional ones, to apply only to the dominant ninth chord; many others use it for any construction of stacked thirds encompassing the interval of a ninth.
Under (b) & (c) are the traditional "dominant major-ninth chord" and "dominant minor-ninth chord." I agree that these labels are preferable as they put the focus on the quality of the interval of the ninth: C4-D5 or C4-Db5. The diatonic seventh chord, with a major seventh C4-B4, is CM7 (some write Cmaj7) or "C major seventh chord": (d) and reinforced with a natural sign at (d*). The CM9 is under (e), and the corresponding minor chords are under (f) & (g).
NB: Unfortunately, I can't make changes to essay files previously published on the Texas ScholarWorks platform.
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