Why does a C7 chord contain a flat note?

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I just don't get it.

Why is it a B flat, and not just a B which is the 7th note of the C Major scale?
09, 05, 2007: Searching for my own voice...
10, 09, 2011: My voice lies somewhere at F# (least used musical key in musical history)
Maybe I'm just too infrequent

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C7 stands for a dominant seventh chord, spelled C E G Bb. Specifically, it is a major triad (C E G) with an added minor seventh (Bb). Theoretically speaking, C7 is the dominant chord in the key of F Major, which has one flat (Bb). If you are familiar with using Roman numerals, in the key of F Major, C7 is the V7 chord.

The symbol for a major seventh chord is CM7, which would be spelled C E G B. This would be the tonic chord in the key of C Major (the I chord). (For sake of completeness, a CM7 chord could also be the subdominant chord in G Major (the IV chord).

As to why the chords are named like that, with a major seventh chord requiring the extra "M"…it is a matter of chord naming conventions that are over a hundred years old… someone with more music history knowledge could go into better details than me…

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Great explanation above!

See here for more explanation of chord types - the original ChordSpace is a great learning tool, too.

http://www.chordspace.com/ChordTypes.htm

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in your 4 note jazz theory any dominant 7 is the V7 chord of a given scale -- all the other chords of given scale are minor or major or diminished -- made up of the notes in that scale/key

it gets a little more involved with minor scales/keys since the V7 in a minor scale seesm to be cheating a little
the whole up/down different minor scales, but bring along the flattened 9th and teh intent toward resolution of the V is clear enough

the naming convention for minor and major 7th chord symbols gotten to the point that most texts have a paragraph or two at that let you know what symbols they'll be using. The dominant 7 like C7 is one of the few symbols that's maintained some clarity

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wrench45us is right, in Mark Levine's Jazz theory book he goes on a bit of an explanation on naming conventions and abreviations on 7th chords. I guess it's just a convention.

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I didnt see any one truly answer the question so here goes.............

Using the conventional system of making chords happen we take every odd note of the mode. In essence we skip every other note to make chords. What was found is that in every major scale on the V mode(mixolydian mode) is when the chord was extended beyond a triad (three notes) into a four note chord. A flat seven would show up instead of the usual 7th (maj7th, delta what have you). This creates the dominant 7th chord with a spelling of 1, 3, 5, b7 instead of the usual 1,3,5,7 (major 7th).


All 7th (as in the dominant variety and not the minors or majors) have a flat 7th in them. So from c thats where you would get the bflat. Or in the case of eb you get db etc...

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The real short answer is that the C7 chord doesn't go in the key of C. It would fit in the key of F. If you're in the key of C, and you add a seventh to the C chord, you get a Cmaj7, which has the B natural. If you're in the key of F, and you have a C chord and add the seventh, that seventh would be the flatted B, which gives you the C7 chord.

Going off on a little bit of a tangent on why we use this: In F, C would be the fifth scale tone. A chord built on the fifth is called the "Dominant" chord. (Forget "why" for the moment, it just is). Now, when that Dominant chord is a 7 chord, you get the famous Dominant seventh chord. The reason we use the V7->I chord change so much is because there's a way our ears expect certain chord tones to move. C7->F moves like this:
C7->F

C->C
E->F
G->F
Bb->A

Notice that you have the "E": that's the seventh note of the F scale, and your ear strongly expects that to move to "F" on the next chord. That's called "resolution": until it moves to F, there's a tension, like something's left unfinished. The same thing happens with the Bb->A, so you've got two strong resolutions in that chord change. This makes it feel very final, so it's extremely common for phrases to end with a V7->I cadence.

Here's the history of music theory in a couple of sentences: music of the Baroque and Classical period was all about using this type of chord resolution, and it's the time when "the rules were written" about how it's used. Beethoven ushered in the Romantic period by messing with this resolution: delaying it to increase tension, or tricking the listener by making it resolve in unexpected ways. This trend got stretched to the point where key became meaningless, which led to the atonal music of the 20th Century.

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BuddhaMaster wrote:I just don't get it.

Why is it a B flat, and not just a B which is the 7th note of the C Major scale?


Because you're forgetting about the major 7th chord, which is the 7th chord which fits in the scale of the root note of that chord. Dominant 7th fits in the scale that has the root of the given chord as the dominant (5th scale degree) of that scale. C maj 7 fits in the C scale, C7 fits in the F scale (C is the dominant note of the F scale).
"You don’t expect much beyond a gaping, misspelled void when you stare into the cold dark place that is Internet comments."

---Salon on internet trolls attacking Cleveland kidnapping victim Amanda Berry

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Damn convoluted is what all your answers are. read my post for a simplified ,correct answer. No of course cdom7 doesn't belong in the key of c. But it doesn't mean that it can't be used there in c. It certainly can and is in this case. In fact you ever listen to a "blues tune"? A lot of dominant 7th in the keys those guys put together. \

to the op;

all dominant 7ths- and I mean all, contain a sound similar (with inversions) to c to Bb.
So on guitar or bass you will always have that shape and the sound of the duad (two notes) that is created when you play c to Bb. Its What is called the flat7. (has lostsa names) All Dominant 7th chords contain an interval called this flat 7th. Also could be a 14th or whatever you have for an inversion.

Seriously folks not the function but how the function got there please.

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Convoluted? Not really. The answer is incredibly simple and it's been covered adequately by several people other than you.

He asked why C7 has a note that isn't in the key of C, and the answer is because it's not the seventh chord built on C in the key of C, C maj7 is.
"You don’t expect much beyond a gaping, misspelled void when you stare into the cold dark place that is Internet comments."

---Salon on internet trolls attacking Cleveland kidnapping victim Amanda Berry

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just throw in a #9 and play a bit of hendrix, hey?
:hihi:

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No the op asked "why is bflat within a cdom7". Fair enough to say ,"well there is no bflat within cmajor and that chord belongs to the key of F." He asked why and again I will highlight why;

Using the conventional system of making chords happen we take every odd note of the mode. In essence we skip every other note to make chords. What was found is that in every major scale on the V mode(mixolydian mode) is when the chord was extended beyond a triad (three notes) into a four note chord. A flat seven would show up instead of the usual 7th (maj7th, delta what have you). This creates the dominant 7th chord with a spelling of 1, 3, 5, b7 instead of the usual 1,3,5,7 (major 7th).


Like another poster said "the short answer is you are playing in Fmaj". I have given a long answer that should be sufficient enough for the op to place dominant 7th chords in there respective keys whenever they choose but more importantly why those chords are showing up in the first place. Which Btw I saw no one adequately do in this thread.

Peace and Grimoires to all you heads out there.

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Honestly I thought this was a very straightforward question and the first reply was just about perfect....

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