Minor major seventh flat five chords: do they exist, and if so, how should they be used?

Question

When randomly playing chords, my husband and I stumbled upon an interesting four-note combination of C, Eb, Gb and B natural, which sounded pretty nice to us despite the dissonance. This looks like a C minor major 7th chord with a flattened fifth (CmM7b5) but i wonder whether this syntax is correct, and/or whether such group of chords exist in practical use (not merely theoretical)?

Additionally, if these chords are used in practice, what are the proper uses of them? (eg. What kind of chord should they resolve into)?

Answer 1

I usually use this chord as an upper structure of a D13(b9) chord:

(D) C Eb F# B

Used in that way, it is an altered dominant chord.

It could also be the upper structure of an Ab7(#9) chord:

(Ab) C Eb Gb B

Of course, this is also an altered dominant chord.

But it can also function as a chord in its own right, i.e. not only as an upper structure. In that case it functions as a diminished seventh chord. All its notes are contained in the C diminished scale:

C D Eb F Gb Ab A B

and the major seventh (B) is a possible tension for a dim7 chord. So in this context your chord would be a Cdim maj7 (even though you leave out the diminished 7th Bbb/A). Try adding the diminished 7th to see if you still like the sound. In this usage, it could resolve to a Cmaj7 chord by chromatic movement of the Eb and F# to the E and G, respectively. This is often done in the first bar of the jazz-standard 'Misty' by Erroll Garner.

As a final note, also note that this chord can be written/interpreted/heard as a slash chord: B/C.

Answer 2

Yeah, I'm pretty sure that's a half-diminished chord. Root-m3-d5-M7 forms a diminished triad, and that Major seventh on top keeps the seventh chord from being completely diminished, so it's "half-diminished." In a major scale, it is the chord that leads to the tonic chord. For example, if I were to play the chord that you found - C half-dim 7 - then you could play a D major after it and it would sorta resolve that dissonance that you noted.

Edit: Oops, it's actually not a half-dim because it has a major seventh on top and not a minor seventh. That's ok, though, because the seventh chord still definitely exists, and it does go with the Dmaj. Try a B-D-F-A chord also, it might sound pretty nice.

Answer 3

Minor flat 5? That's a diminished triad!

But in all seriousness, though I'd call it °maj7, I've seen plenty of use for that chord. Built on the 4th scale degree in major, it makes a nice minor-plagal-ish sound similar to that of ivmaj7 [that's to say, Xm(maj7)]. It can function also very similarly to a fully diminished chord: iii7 to ♭iii°maj7 to iim7 sounds nice in a functional jazz context.

Rearranging and respelling the notes, one finds a potential reason for its functional sensibilities: B(♭9)! The chord contains a major triad, and that can give this set of notes a sense of stability that diminished seventh chords lack.

Another cool thing: This chord can go really well with the G harmonic major scale [G A B C D E♭ F♯ G], and you can make some beautiful sounds out of that.

Overall, the chord seems much more closely related to the diminished tonality than the major seventh tonality, but adds a bit of stability and brightness to an otherwise tense sound. There's no "right way" to resolve this chord, but the above are some ideas on how one might get started experimenting with it. If you like the sound, who's to say you're wrong?