# How would you calculate the name of this C/A# 7th chord?

I'm playing the following voicing of a C7 chord on the guitar:

Strictly speaking this would be denoted as a C7/A♯ slash chord.

But I'm trying to figure out what voicing name this would have.

Is this just a 3rd inversion or some other voicing name?

Let me explain why I'm confused...

A C7 in close position would be:

1 (C), 3 (E), 5 (G), ♭7 (B♭)

For me to construct the voicing shown in the image above, I would (in a practical sense) see that I needed to drop the ♭7 by an octave so it was played on the D string of the guitar. Which would then require me to move the root (C) up an octave (as I couldn't play both the ♭7 and the root on the same string).

In doing that, from a degree perspective, what we have now is:

♭7 (B♭), 3 (E), 5 (G), 1 (C)

Because the ♭7 is now in bass position, this suggests the voicing is a 3rd inversion of the chord. But the remaining degrees are not in order. Does that matter?

e.g. I would've thought a strict 3rd inversion to be [♭7, 1, 3, 5]

On a side note: I've been led to believe there are scenarios where a voicing could be called something like "drop n of n inversion", is that correct? I don't think that would apply to my primary question above. But I believe what I would've called a "drop 2 of Cmaj7" (just for example) could also have been called a "drop 2 of Cmaj7 2nd inversion" because the particular voicing I would likely use on the four high strings - d,g,b,e - would have the 5th degree in the bass position, which by definition is kind of like a 2nd inversion of the chord...

• Is that picture supposed to be a guitar fretboard? Sep 10, 2021 at 19:29
• You seem well aware that the 7th is b7. So how could it be A#.?A is the 6th, making B the 7th. So now that note needs to be called Bb. I suspect it's a guitarist thing, whereby the 'black notes' always get called sharps...
– Tim
Sep 11, 2021 at 11:37
• I took out all the code blocks since they aren't necessary - it's fine to just type out letter names, or I like to use braces for when grouping is necessary. Code formatting can screw with screen-readers and other accessibility tools and stuff, so we try to avoid it when not necessary. Plus the blocks were preventing some of the examples from rendering properly. Sep 13, 2021 at 6:10

## 6 Answers

The lowest note played in a chord denotes its inversion, regardless of the order of the higher notes, Thus, in C7, root position has C at the bottom, 1st inv. has E, 2nd inv. has G and 3rd inv. has Bb. The other notes need to be there (with the exception on occasions of 5), to constitute the named chord, of course.

It would be called C7/Bb (not C7/A#,as A# is an aug 6, we need b7).

On guitar there is sometimes a problem in that certain voicings cannot comfortably be fingered, thus a 5th may need to be left out, and sometimes it makes sense to double other notes, usually an octave apart.

There is a naming system called 'drop x' which you are aware of, and this is how the voicing you mention gets named.

Incidentally, you mention Cmaj7, which on guitar at least, doesn't sound good with a C note on the top string. The other inversions work well, but that one just doesn't seem to sound convincing.

Forgive the slightly pedantic answer, but this could be an A♯ in the bass and not a B♭. Spelled with an A♯, this becomes the "root-position" German augmented-sixth chord A♯–C–E–G.

While a C7 chord (with this pitch spelled as a B♭) will often resolve to an F chord, the augmented-sixth spelling will often resolve first to a B chord (or an E/B) and then to E. This is because this augmented-sixth is a predominant in E, and thus it moves to its dominant and then to tonic.

This is a relatively rare chord in the classical style (let alone in a popular style), but I think it's worthwhile to include it as a possibility.

• not root position: A# to G is a diminished seventh. C to A# is an augmented sixth. This would be third inversion. Sep 10, 2021 at 12:53
• @Aaron Yes, this is why I put "root position" in scare quotes. There are different views to it: some view C as the root, some view A♯ as the root (from a stacking-thirds standpoint), and others (myself included) consider it a chord without any real root at all.
– Richard
Sep 10, 2021 at 13:18
• ... or resolving ti Em/B Sep 10, 2021 at 21:05
• Interesting, but extremely doubtful! Most guitarists aren't aware of German 6ths, but most guitarists are aware of dominant 7ths - even though they don't spell it correctly!
– Tim
Sep 11, 2021 at 11:41

German augmented-sixth chords notwithstanding, this is a common guitar voicing for a C7, and it is a member of the drop-2 family of voicings. I would call it a "drop-2 in third inversion", but you could also call it a "drop-2 of third inversion"; either is correct. I wrote at some length about drop voicings on guitar in this answer.

Here are the drop-2 voicings of F7 on the top four strings; I chose F7 instead of C7 for this illustration since this makes it easy to start from root position and move up the fretboard to the subsequent inversions:

``````%X/X.X/X.3/1.5/3.4/2.5/4[F7]    %X/X.X/X.7/2.8/3.6/1.8/4[F7/A]
``````
``````%X/X.X/X.10/1.10/1.10/1.11/2[F7/C]    %X/X.X/X.13/1.14/2.13/1.13/1[F7/Eb]
``````

The shapes for C7 are the same as those above for F7, and you can see that the shape of the final F7/Eb matches the shape of OP C7 moved from the 8th fret to the 13th fret. On a chart I would probably only write F7; if the inversion really matters I would write, e.g., F7/Eb. But I wouldn't write out "F7 drop-2 in third inversion"; if the particular voicing is that important, I would just write it out on the staff.

• Do you know the history or origin of the "drop" voicing terminology? I've played guitar since about 1975 and never encountered it. (Most of my theory education has been more pianistically inclined, so that may be why it is unfamiliar.) It seems odd, especially the way it's numbered from the top. Of course for someone who started on piano, learning theory on guitar seems to make as much sense as doing accounting work with Roman numerals. Sep 10, 2021 at 17:19
• @Theodore -- that's a good question, and I don't know. Piano players talk about drop voicings, too, but maybe its mostly a jazz thing. It's really just a systematic way to think about some useful 7th chord voicings; since they are useful, a lot of people know some of them without knowing the drop-n business.
– user39614
Sep 10, 2021 at 17:36
• @Theodore You might already know this, but I believe it comes from the voicings that involve taking a close position (stack-of-thirds) seventh chord, then dropping the second note from the top down an octave. Why they chose to start counting from the top note, though, I have no idea. They also have drop-3 and drop 2&3, although those get weird on guitar I believe. Sep 10, 2021 at 22:22
• @user45266 -- the drop-n nomenclature definitely comes from the mechanical procedure for forming these voicings (which I described in some detail in my linked answer), but I don't know when this terminology came into common use, or really anything else about its historical origins; I do think that it is an interesting question, and I'd be interested if someone had some insight into that.
– user39614
Sep 10, 2021 at 22:30
• Ah, you got me, somehow I missed that answer link. And on my own question, too - how embarrassing! :) Very interesting for sure. If you want to ask it as a question I'd be delighted to see where it ends up. Sep 10, 2021 at 22:33

Strictly speaking this would be denoted as a C7/A♯ slash chord.

Strictly speaking it's `C7/Bb`, there is no `A#` in a `C7` chord.

Yes, it's third inversion.

It's an open voicing. In terms of "drop" voicing it's "drop 2" voicing. To get "drop" voicings, number voices from 1 starting with the top voice going down, then "drop" voices by lowering them by an octave, like this...

Because the ♭7 is now in bass position, this suggests the voicing is a 3rd inversion of the chord. But the remaining degrees are not in order. Does that matter?

Not in regard to the inversion. For that you only need to know which chord tone is in the bass.

After the bass, the arrangement of the remaining chord tones in various octaves will determine first whether the voicing is "close" or "open", and if it is "open", the "drop" terminology is the only standard for distinguishing specific spacings.

In terms of basic harmonic function only the root progression matters. All the rest of how individual chords are voiced is a matter of taste of how you like the intervals stacked vertically or a matter of voice leading regarding how chords connect in a progression. For example, any voicing of `C7` to `F` is just functionally dominant to tonic, but `C7/Bb` to `F/A` brings in voice leading - specifically telling how the bass moves - then the specific voicings of the upper voices is mostly a matter of taste, unless they're specifically notated in some way. Lead sheets don't normally give voicings.

It would be interesting to have this chord in a context, e.g. G or Em.

It will be ii7 of G resp. iv7 of Em (with augmented root) resolving to BDG or BEG or B,D#,F#.

now you can say for easier reading this is C over A# but indeed this was A,C,E,G -> A#,C,E,G (chromatically transformed), so we have a dim3, dim5 and dim7, A# dim,dim,dim or A# diminished double dimineshed. I'm afraid nobody would understand this labeling.

It's simpler to describe it like Richard says as a Gerd chord , developed historically from Am7 (1st inversion=C,E,G,A)-C,E,G,A#, in "root position", an altered chord in G major or e- minor, functioning as a secondary dominant.

Inversion naming depends only on what the lowest note is. It tells us nothing about the voicing. So yes, it's C7, 3rd inversion.

If you wanted to describe the voicing, 'raise 2' might seem more appropriate than 'drop 2' :-)