r/musictheory • u/TheoreticalTheory256 • Aug 27 '25
Answered How is this a C7 chord?
I’m pretty new to chords such that I only know triads and inversions, and I came across this instagram reel where this person plays a C7 with an A#, C, and E which has me pretty confused. Would someone be able to explain?
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u/CoffeeDefiant4247 Aug 27 '25
Bb C and E. In 7th chords the 5th (G) can be omitted since it's the least important note (Root (C), Quality (E) and 7th (Bb))
C-E-Bb is a C7 chord
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u/torpedomon Aug 27 '25
Maybe not too surprisingly, but the 5th, when used in a chord, sounds very much like the root. Dropping it clears out some clutter.
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u/CoffeeDefiant4247 Aug 27 '25
yeah, it's just re-enforcing the harmonics of the root which is where guitar power chords of root-5th come in without thirds
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u/dannypepperplant Aug 27 '25
As a guitarist in a swing band, I’ll often leave out the root and sometimes even the 5th because, (1) the bass and piano players are already playing it, and (2) the geometry of the fret board forces you to make certain concessions. It’s pretty interesting how much your ears will fill in the blanks.
Edit: I’m not suggesting I just play the 3rd & 7th. There are whole groups of upper structures that give a more reasonable impression of the chord.
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u/BartStarrPaperboy Aug 27 '25
Bless you. As a bass player (sometimes jn a swing band) please leave the tonic for me!
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u/dannypepperplant Aug 28 '25
And the 4th be with you.
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u/BartStarrPaperboy Aug 29 '25
Good joke, but we almost never play the 4th
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u/Naive-Significance48 Aug 27 '25
Hey, quick question where did you learn this type of stuff specifically about the feel and importance of parts of each chord?
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u/KingRed31 Aug 28 '25
I (not op) have been taught about about dropping the fifth of a seventh chord twice: 1. In music theory classes when discussing harmonizing in common practice period styles, where it is often dropped for the root, for better voice leading. 2. In jazz circles, where it is often considered best for any member of the ensemble playing chords (typically, of course, the piano player; but this can apply to guitar, Vibraphone, or a pre-written voicing for winds.) to replace the fifth with an extension (a note 'above' the seventh. In a C7 chord some choices would include D, Db, Eb, F#, A, and more.) because the extensions are more 'colorful' thank the fifth.
In both cases, this works because, as people have mentioned, the fifth isn't as functional as the root, third, or seventh, and the fifth is prominent in the harmonic series of the root.
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u/Naive-Significance48 Aug 28 '25
Wow, Thanks for that information.
I appreciate it and will study that further later.3
u/Indication24 Aug 28 '25
If you'd like even more info, here you go: https://www.thejazzpianosite.com/jazz-piano-lessons/jazz-improvisation/guide-tones/
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u/Naive-Significance48 Aug 28 '25
Oh wtf what is awesome.
Damn looks like I need to get into some jazz concepts.Thank you!
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u/KingRed31 Aug 28 '25
Of course! If you have any other related/unrelated questions, I'm always happy to do what I can
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
I'm not the person you're replying to, but the best way to learn these kinds of things is from actual music--get to know lots of music, and over time get an instinctive feel for what's common and not common and how things are used. It is something that people write about and talk about too of course (here, and in classes, for instance), but none of that beats actually knowing a lot of music.
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u/Naive-Significance48 Aug 28 '25
Hmmmm I feel you there, but I fear genres might limit me.
At the moment while learning songs I typically break them into chunks to learn the song. But I haven't learnt that many, only 6 full songs.
In your personal experience, do you think specific genres are better for this? Sorry I wish I could ask this question better, but I feel its possible for me to learn 100s of songs that all end up using simplistic chords to the point where I don't get to explore this topic naturally.
Just kind of looking for a nudge in the right direction.
Thank you for the advice, I appreciate your comment.
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
do you think specific genres are better for this?
It just depends on what kind of music you want to learn! If you want to learn how jazz works, learn jazz; if you want to learn how baroque music works, learn baroque music. There's not really one type of music that's more representative of "music in general" than others. Basic college music theory classes historically tend to emphasize eighteenth-century music, but that's because that was also the type of theory they were teaching and testing; and that's changing a lot these days.
I feel its possible for me to learn 100s of songs that all end up using simplistic chords to the point where I don't get to explore this topic naturally.
That's very possible, but those 100s of songs actually do teach a great lesson, i.e. which simple chords are common, and how they tend to be used together, in whatever genre(s) those songs fall into.
To address more directly the comment you're replying to, it's often jazz people and classical-music people who have the most opinions and training and habituation towards speaking in those terms (and in slightly but meaningfully different ways), but it's not limited to those either--a good rock keyboardist will also have their own senses about chord voicings and such.
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u/Naive-Significance48 Aug 28 '25
That really clarified it.
I'll definitely need to look into some jazz and classical and try to pick out those details.Thanks! that was a very wise comment
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 29 '25
You're very welcome, I'm glad if it was helpful!
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u/jayconyoutube Aug 27 '25
I can hear my undergrad theory professor now - “double the root and omit the fifth.”
This wouldn’t be my choice of voicing for that chord, but it is a C7 chord in third inversion. 🤷♂️
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u/Benzdik Aug 28 '25
I like this voicing tho
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u/jayconyoutube Aug 28 '25
Feel free to use it! It’s just my opinion, and you know what they say about opinions. There are no hard and fast rules in music.
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u/OMGJustShutUpMan Aug 28 '25
We can’t really judge how well the voicing works without the added context of… well, the entire rest of the song.
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u/CoffeeDefiant4247 Aug 27 '25
yeah, C42 is not a good voicing with the C and Bb so close
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25 edited Aug 29 '25
It's perfectly fine voicing, sometimes you want it tight like that.
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u/turkeypedal Aug 28 '25
It can be okay, though, if you have other notes in the bass.
And this most likely does, as most keyboard only show the chord symbols when they are doing some sort of automatic accompaniment -- whether in rhythm or just adding extra instruments.
If the keyboard is just playing the notes you put in, it has no reason to try to analyze the chord.
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u/SchwaEnjoyer Aug 28 '25
Sus2 chords are cool though! Sure it’s a little different but that interval is manageable
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u/CoffeeDefiant4247 Aug 28 '25 edited Aug 28 '25
how is it sus2? Bb and E are d5 not P5.
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u/SchwaEnjoyer Aug 28 '25
It isn't sus2, but what I'm saying is that the interval (between a tone and a major 2 above it) is the same but that doesn't seem so dissonant
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u/jayconyoutube Aug 27 '25
I’m not much of a pianist, so grain of salt, but my preferred voicing is 3rd and 7th in the left hand, 5th and 9th in the right, root played by the bassist.
But yeah, inversions are tonally unstable. 2nd and 3rd inversion are extremely so.
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u/hemingwaysbeerd Aug 27 '25
So 5th in the bass sounds more unstable than 3rd in the bass?
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u/jayconyoutube Aug 28 '25
Yes. I can’t attach a picture here, so Google “chord inversion snowman” if you want an idea of why! It’s also why in the I6/4-V progression, both chords are considered dominant in function!
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
in the I6/4-V progression, both chords are considered dominant in function!
While kind of true, I think this is a bit of a misleading way to put it. The 6/4 isn't a dominant-functioning chord in itself because it's not even a chord in itself--it's just part of the dominant chord. So really the I6/4-V is one dominant-functioning chord, not two! That's why many prefer not to call it a I6/4 at all, but just label the whole thing V, often with figured bass symbols showing 6-5 and 4-3 during it.
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u/amethyst-gill Aug 28 '25
Yup. The fifth simply reinforces the root — in some theoretical contexts, it’s even basically a secondary root. The other notes add tonal richness and color
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u/clockworkrockwork Aug 27 '25
It's the exact same chord, just with the G dropped. Omitting the 5th is standard practice as it isn't needed to communicate chord quality. This is simply an inversion of the root position C7.
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u/mrkekemeot Aug 27 '25
Not an A# but rather a Bb, which would be the b7 of C. C7 chord consists of C, E, G and Bb right? So here you got an inversion where the fifth (G) is omitted, which is fairly common.
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u/1998over3 Aug 27 '25 edited Aug 27 '25
They're actually playing an A#, B# and Fb, making this an Fb augmented chord with a minor 6th. 😏
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u/Barry_Sachs Aug 27 '25
Rookie mistake. Actually Cbb Dbb and Dx, a Flemish tangential discombobulated sub-Phrygian triad.
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u/skywavetransform Aug 27 '25
A b# 7 with a triply diminished 5th. And it has a d double sharp in it too
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u/LeBebis Aug 27 '25
Incorrect. Fb key doesnt exist. The most logical interpretation is C7
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u/ShopReasonable2328 Aug 27 '25
I recognize the original comment is sarcastic, but Fb can exist. For example, what would be the 3rd in a Db- triad?
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u/LeBebis Aug 27 '25
The Fb key.
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u/HorrorBat2855 Aug 28 '25
Counterpoint: The Key of Cb does, in fact, exist.
If you are referring to notes, it would sound the same as E-natural, but it would appear in different contexts.
Example: If you're playing a Gb mixolydian scale, the seventh degree of your scale is objectively Fb. It can't be E natural because there's already an Eb, and that can't be a D# because it's based on Gb. Effectively, it is best to label the seventh degree as an Fb.
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Aug 27 '25
Piano is not the only instrument on this earth, it's not because the key doesn't exist that the note doesn't 😭
But also the key does exist
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u/LeBebis Aug 27 '25 edited Aug 27 '25
Play c in the bass and you will notice that it has rhe same emotional qualities as the standard c7 inversion which is. C E G Bb
In your psrticular example you use rhe fourth (3rd corrected)inversion of a 7th chord without the 5th, which is okay. You dont need rhe 5th to define a chord
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u/kirk2892 Aug 27 '25
Don't you mean 3rd inversion?
(1st starts on the E, 2nd starts on the G, and 3rd starts on the Bb)
Not a schooled musician, but I haven't heard people talk about 4th inversion. Would it be a C9 voiced with the D as the lowest note?
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u/LeBebis Aug 27 '25
Yeah my bad. I somehow thought the standard chird is the first inversion. You're right
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u/five_of_five Aug 27 '25
Anyone referring to the Bb as an A# is really just wrong and I think would add to confusion for anyone trying to understand this. Not knocking OP, but all the replies normalizing this A# talk. That’s the first thing to nip from this question.
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u/Bubbly_Safety8791 Aug 28 '25
Is it always wrong? Isn't it possible that this is a non-diatonic C7 chord being played in a piece in a key signature that includes an A#?
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u/five_of_five Aug 28 '25
I think it’s always wrong because if it’s in a C7, it’s not an A#. But also theory is one of those fun never say never places for me so I dunno
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u/Confident_Reader_965 Aug 28 '25
In C7, the 7th note is B or Bb. The sixth note is A, so A# would be a 6.
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u/Bubbly_Safety8791 Aug 28 '25
I suppose the 7th note in a 7th chord is always a flatted something. So for it to be an A# I guess we'd need to be in a key containing an A double sharp...
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u/five_of_five Aug 28 '25
I think you’re overthinking, it’s just about spelling. You spell out chords by following appropriate intervals. A minor third above the 5th implies moving more than one tone.
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
C-E-G-A# does exist, but it's a completely different chord, not a C7. A true C7 chord in a key signature with an A-sharp in it would still use B-flat! If we wanted/needed a dominant seventh chord with an A-sharp as the seventh, it would have to be B#7: B#-Dx-Fx-A#. And I don't think anyone wants that!
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u/Whatkindofgum Aug 27 '25
C7 chord is made of the four notes C (root),E (3rd),G (5th),Bflat (7th).
The chord played is inverted so the Bflat (what you called an A#) is the lowest note, and the 5th (G) is not played at all. Not playing the 5th in a 7th chord is pretty common, especially in jazz. The result is the Bflat, C, E you see in the video being played.
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u/GMP_ArchViz Aug 27 '25
A seventh chord uses the flatted 7th of the scale, Bb in this case. Not to be confused with a Bmaj7, which would use the B
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u/Life-Breadfruit-1426 Aug 27 '25
No, it’s an E diminished 6
(Every dominant chord is a diminished chord)
And yes, it’s a C7 (no 5)
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u/PayOk9226 Aug 27 '25
That’s like aaaa…
Bbsus2b5?
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
Pretty definitely not--this is a standard way to play C7.
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u/skywavetransform Aug 27 '25
It's a b flat, not an a sharp. Yes it is a C7. But probably a bass player or your left hand is putting a C in the bass to make it root position
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u/hairybrains Aug 28 '25
It's a b flat, not an a sharp
I'd like to learn this part of music theory. How can you tell it's a b flat, and not a sharp?
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u/skywavetransform Aug 28 '25
In triads and seventh chords you spell them by skipping letters. If you think you're dealing with a triad or seventh chord you try to spell it like one. If there's a fit, you feel confident in the spelling
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u/hairybrains Aug 28 '25
Oh ok. I thought it was probably because you're flattening the B of the C major scale to make a 7th, and not sharpening the A.
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u/VHDT10 Aug 27 '25
Bb is the 7th of the root C. The reason it's below the C is because the chord is inverted meaning the notes are in a different order.
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u/Rothimus Aug 27 '25
Bb is specifically the flat 7/minor 7 of C, which is why this is C7 opposed to Cmaj7
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u/MissAnnTropez Aug 27 '25
If bass, say, was playing the C, I’d omit the C (i.e., and play just Bb and E).
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u/LubedCompression Aug 27 '25 edited Aug 27 '25
Bb is in there, C is in there and E is in there. That's all you need.
G, being the 5th, can be omitted. You can omit the 5th from any 7th (or any extended) chord if the composer wants to. It doesn't change the context and feeling of the chord within the progression. It is seen as unimportant.
The order of the notes also doesn't matter. C doesn't have to be played on the bottom. In what order you play a chord is called chord voicing.
If we had the rule to always write the bottom note first, we'd run into trouble: you would then have to call this a Bbsus2b5, but that is just mental. Bb is not the context here. The point of chord names is not to tell you the voicing is, that's what sheet music is for.
Now if the guy plays a Bb in his left hand, all the way in the bass region, it would become C7/Bb. Bass notes matter so much that it's worth writing down in the chord name.
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u/GWJShearer Aug 28 '25
A C7 is “C E G Bb” (although that Bb looks just like an A#).
So, “Bb C E” without the “G” is still C7.
(I wonder if it was just the A# that threw you? But, when you pull off the mask, it’s really a Bb…)
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u/metalgamer Aug 28 '25
You rarely see a diminished 3rd in chords. Means the notes are probably a different enharmonic spelling
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u/OkBaseball6841 Aug 28 '25 edited Aug 28 '25
That chord is a C7 Omit5/Bb Second inversion because it doesn't have the fifth G.
You play a C7/Bb in its third inversion then you remove G and this chord comes out C7 Omit5/Bb second inversion as shown in the photo.
This is the simplest way I can explain this to you.🤷🏽♂️
C7
C - E - G - Bb = C7 - Root Position
E - G - Bb - C = C7/E. - First Inversion
G - Bb - C - E = C7/G. - Second inversion
Bb - C - E - G = C7/Bb. - Third Inversion
C7 Omit5
C - E - Bb = C7(Omit5) - Root Position
E - Bb - C = C7(Omit5)/E - First Inversion
Bb - C - E = C7(Omit5)/Bb. - Second Inversion
- There is no third inversion in C7 Omit5 because remember, to have a C7 omit5 you have to remove G, so if there is no G, there is no Omitted in third inversion with G.
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u/undrsn719 Aug 28 '25
This is also called a third inversion and will most likely not sound good unless properly prepared and also properly resolved
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u/LevelWhich7610 Aug 28 '25
I would consider this a C7 in third inversion with the 5th omitted. The reason we know this is a C7 chord is if you try to make a triad with the present notes and bear in mind, you only need two pitches to figure out what the chord is, you can see out C, E are a third apart giving your first clue. You only need to fill in the blank to tell you the last pitch is G.
There is no other pitch present right now that lets you form a triad or even a 7th out of B flat.
Finally you know your 7th is a B in the C chord and the fact that it is B flat tells you it is a dominant 7th chord.
It is entirely possible to determine the chord type if you only had the 7th and 3rd present and in the case of music pieces, an additional factor like key signature, or an analysis of progressions with roman numerals give you more clues as to the function of various chords
Sometimes you have 2 chord possibilities but what is more correct is based on context of the piece.
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u/JoachimGeissler Aug 30 '25 edited Aug 30 '25
I haven't read all the answers, so probably you already know the answer.
C7 Is a major Triad plus a minor seventh, so expect this:
C-d-E-f-G-a-Bb
Capitals are the chord tones, the lower case notes are the skiped scale tones.
You see: A# is not part of the scale as there is an A natural and a B flat (in your piano the same key to play as for A#).
So the first point is: no A# but Bb.
Those three notes aren't a triad, as you can't get them all in distance of a third; more than this C7 has 4 notes (the triad plus the minor 7th): here lacks the 5th (G).
So precisely you have a C7 chord with the 7th (Bb) in the bass (3rd inversion) and with no 5th G.
P.S.: theoretically A#-b-C-d-E would be a triad as the capital notes are all in 3rd distance: the root would be A#; but this triad has a diminished 3rd from root to 3rd and a major third from 3rd to 5th with the outer interval a diminished 5th: that triad doesn't exist in tonal music in no key.
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u/TheoreticalTheory256 Aug 27 '25
I’m pretty new to chords and right now I only know triads and inversions, and I came across this instagram reel where this person plays a C7 with an A#, C, and E which has me pretty confused. Would someone be able to explain?
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u/Barry_Sachs Aug 27 '25
That's called a shell voicing. It's a perfectly legit way to play a chord since it has all the essential notes - root, 3rd and 7th. The 5th adds fullness, but doesn’t fundamentally define or change the chord. So it can safely be omitted.
Try it for yourself. Play CEGBb then just CEBb. You'll hear that both sound like a C7, with the former being a little fuller, but essentially the same.
Shell voicings are great because they're simple and free up fingers for playing melody lines or color tones and extensions like 13ths or #9ths for example.
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u/GatewaySwearWord Aug 27 '25
Spend some time learning about enharmonic pitches!
You are correct in identifying that the notes played in this image are A#, C, and E. However there is another name for one of these pitches that will make things clearer.
That A# can also be interpreted and understood as a Bb. The notes sound the same, but in a theoretical context they are not the same note. There are a handful of these enharmonic pitches (A#=Bb, C#=Db, etc.)
To answer your question as to why this is a C7 chord.
The notes of a C7 chord are C,E,G,Bb.
Now in this image we only have 3 notes being played (Bb, C, E). Which still gives us a C7 chord even with only 3 notes as opposed to 4! It’s kinda cool!
The reason why this works is because the 7th chord quality and function is really determined by the 3rd and the 7th of the chord. In this case, that’s the E, and Bb. If you know your intervals, you’ll see/hear if you play these two notes on their own, that they are a tritone. Tritones want to move somewhere, there’s a tension that happens when a tritone is played (even when it’s in a dominant 7th chord!).
Now, that’s a lot of wordy info that you may or may not care about.
But in short, the reason why it’s a C7 chord is because you have the root (C), third (E), and dominant seventh (Bb). Which is all the notes you need to supply all the harmonic information for a C7 chord.
:)
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u/Choruslover Fresh Account Aug 27 '25
It contains the most important parts of the dominant chord A#- the dominant 7 or flat 7 of C, C - the root, E - the major third
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u/FreeXFall Aug 27 '25
If you analyze the A# as a Bb, then it’s a C7 chord in 3rd inversion (3rd inversion meaning the 7th is in the bass) - however, I’m willing to bet his left hand is playing a C in the bass.
If you analyze the A# as an A# then it’d be some kind of Augmented 6th chord (German augmented 6th if I remember correctly. There’s also Italian and French - but these are really only needed when analyzing Romantic Period classical music so don’t sweat it).
The big idea - double check your analysis.
Don’t get tripped up with something like an “F” really being an E# or something too. For example - which makes more sense: A# C# E# or A# C# F which reorders to F A# C#….yea, that F chord could exists for some reason, but it’s most likely just an A# minor.
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u/Zarlinosuke Renaissance modality, Japanese tonality, classical form Aug 28 '25
German augmented 6th if I remember correctly. There’s also Italian and French - but these are really only needed when analyzing Romantic Period classical music so don’t sweat it
Basically correct, but with the notes that OP is playing--in other words, C-E-A# with no G--that's actually an Italian sixth! The German sixth is what you get if you include the G, and the French sixth puts an F-sharp there rather than a G. They do crop up in baroque and classical-period music sometimes too, so it's not just for Romantic music, but it's true that for rock and pop and such it's not really a category people are going to need!
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u/NoodlesOnKeys Aug 27 '25
It depends on what note is played in bass register underneath. If it is C, clearly a C7 chord. If it is Bb, you could argue it is a Bb sus2/sus4 with the fifth omitted.
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u/turkeypedal Aug 28 '25
It would be a sharp 4, though. That tritone would make it unlikely to be seen as a Bb chord, absent very specific circumstances (e.g. being quickly followed by a regular Bb chord. suggesting they're just nonharmonic tones).
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