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Thread: theor question?C9 and Cm9; question about the Bb in the chord structure.

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    theor question?C9 and Cm9; question about the Bb in the chord structure.

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    I am building a chord chart for playing guitar where I draw out the chord on the strings on a guitar so I have an understanding of what role each finger is responsible for in a chord. I will understand theory better as a result as well as a deeper understanding of my fretboard.

    So for a C major chord I understand the theory CEG and for a Cminor chord, I need to flat the 3rd (Eb). I also understand that in a C9 chord and a Cm9 chord that adding a "d" into the chord is what makes it a C(9) chord and Cm(9) and gives it that "9" tonal characteristic. What I don't understand is how/why a Bb is part of that chord structure. Why are any notes needed other than C,E,G,D for major 9 and C,Eb,G,D for the Cm9. And IF we need another note why Bb? Thank you.
    Last edited by dksucharda; 06-20-2019 at 10:49 AM.

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    Technically, a 9th chord would need the dominant 7th as well, which is why you would play C, E, G, Bb, and D. Many people leave out the 7th, however, to make it easier to play and to “avoid clutter.” When playing this way (and playing the D right next to the root C, as opposed to an octave up on the piano, for instance), you can also call that “9th” chord an “add2,” as in “Cadd2” or “C2.”


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    rhthmgj, thanks for responding. I completely follow how this could be called a "add 2" and I understand that commonly the 7th is commonly left out to "avoid clutter" but what I still don't understand is why is it even part of the chord "equation" at all? I also don't understand why if it is in there, why is it flat. If we are talking the Cmajor scale and there are no natural flats or sharps why would you the 7th be a Bb. I might be wrong in my thinking but usually I think of a chord as being a triad of either major or minor and then you add other characteristics to it for achieving the sound you want (sus 2/4, min7b5, aug, dim) which I understand. but in this example in addition to the CEG and the D for the 9th why is the 7th part of the equation? I know I i am being technically picky, I am just trying to REALLY understand this stuff. Thanks for ;your help and patience.

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    Theoretically, a 9th chord automatically includes the 7th, an 11th includes the 7th and 9th, a 13th the 11th, etc. In practice, not so much. But it does make sense if you think about it. You don’t drop the 5th just because you’re playing a 7th, right? (no matter the chord quality or number of extensions— dominant 7th, Maj7, etc.). Same thing.

    When you play a 9th, technically you are adding a 9 to a 7th. When you play an 11th, you are adding that to a 9th chord (that also theoretically already includes the 7th).

    Maybe these links will help:

    Chord spelling

    Jazz Guitar Chord Theory - How To Construct Jazz Chords?


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    ok, I buy that explanation, makes sense. Thank you, but for me there is still one question that remains. If we are in the key of C and are using notes from that scale to build a scale why is the 7th a Bb and not just a B?

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    Because that would be a Major 7th. What most people call a “C7” is actually a “Cdom7” (C dominant 7th); likewise a Cm (C minor) with an added 7th would be a “Cm7” (C minor dominant 7th), unless you really wanted a CmM7 (a.k.a. C minor Major 7th). Also expressed using the “triangle symbol” for major...


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