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In terms of a major scale, I heard that the I and IV chords can be maj7, the V chord is dom7 and the ii, iii, and vi chords can be min7. Would the same logic apply for 9th chords?

  • Good question: although I know that V9 can be used in the same way as V7, I suspect I9 creeps dangerously into sus-chord territory, and I'm not sure whether it can be used in the same way as I7. – Dekkadeci Dec 25 '18 at 9:53
  • @Dekkadeci - I9 can't be a sus chord, as the M3 is included. It's not even going to be an 'add9' chord, as there will be a 7th in there too. Without the 7th, it's an add 9, but still with M3. Only losing that M3 could make it a sus. – Tim Dec 25 '18 at 10:09
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    @piiperi Actually I am deaf, so I don't trust my own ears. Thank you for your help I guess. – Rusty Shackleford Dec 26 '18 at 4:04
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    @Rusty I'm sorry, that was an unhelpful comment, I deleted it. I just have a bit of a hard time understanding the conditions where questions like this arise. In a way it's like "could someone please try this chord and let me know what it sounded like". But if you're actually deaf, then that would indeed be the case. – piiperi Dec 26 '18 at 9:54
  • @RustyShackleford, are you asking in reference to strictly diatonic progressions? Because the in 12 bar blues (I, IV, V) all three are dom7 chords, and the 9th works on all 3. – ggcg Dec 26 '18 at 16:03
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Basically, yes. Each is an extension of the process of adding thirds.

With I9, it's a major 9th, IV9 also. V9 is dominant.

vi9 is minor 9th as is ii9. iii9 is also m9, but with the 9th note non-diatonic.

  • Thanks Tim, for making this deaf man's life a little bit easier! – Rusty Shackleford Dec 26 '18 at 4:40
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I use maj9 chords for things like this:

  • thicker maj7 (i.e. I use it in my cooking the same way I'd use a maj7, but it makes the result feel denser)
  • even more elevatorish than maj7
  • stronger tonality-setting than maj7
  • fast way to Girl from Ipanema, Last Christmas, and similar songs
  • the 9th tone is a bit superfluous, so it can be used for rhythmic texturizing voice movement without actually doing anything harmonically substantial (i.e. you can usually add stuff like that for texture or for your own amusement without negotiating with others, and it won't ruin the harmony). Sort of like what you can do by adding a 2nd, but when it's the highest note of the chord, it has more room to move without getting too close to the 3rd.

By stronger tonality-setting I mean, play the chords: B - F (i.e. major chords a tritone apart, so the combination shouldn't make much sense). Then compare with Bmaj7 - Fmaj7. Then compare with Bmaj9 - Fmaj9.

The maj9 version makes me feel the most at rest ("stable" might be the correct theory hygienic word) on both chords, and even the tritone jump doesn't feel as harsh. The feeling of stability might be explained to come from there being more notes of the scale, so it's more explicit and leaves less room for imagination.

How about, now you go and try some uses for the maj9 chord yourself?

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