A C7 chord is wrong, it’s miss-named and quite frankly it is about time someone did something about it. One of the most common topics I find myself having to repeat to students when teaching theory is ‘7’ chords. More specifically, it is the difference between a C7 chord and a C Major 7 chord that most students struggle with. For guitarists it can often be left at the difference in shape— little finger down to make a C7, 1st finger lift off to make a CMajor7 — but when we come to understand the theory of chords, it becomes something of a stumbling block for many. So here we go, let’s put this one to bed and sort out the difference between a 7 chord and a Major 7 chord.
I am using C7 and CMajor7 as the examples throughout this. The theory itself can be applied to any of other 7 or Major7 chord; D7, A7, BMaj7, EMaj7 etc.
The Simple Answer
There is a simple answer to this and a slightly more long winded version. I’m not going to make you read through another thousand words before giving you the simple answer, I will give you the simple answer first. If you are interested in the full explanation, go ahead and read the rest of this post, if not then here you go.
A C7 chord is actually called a CDominant7 chord and in essence means:
A C Major triad (C,E,G) with the flattened 7th note of the C Major scale on top.
Yes, that’s right, dominant means flattened, I don’t know why*, I didn’t write the rules here, I’m just helping you understand them. Why they didn’t call it a C(b7)? I don’t really know, but they didn’t, and we need to live with that.
*I actually do know why, we just don’t need to worry about that here.
A C Major triad with the 7th note of a C major scale on top. (I.e. un-flattened).
Here’s those two chords shown against the scale:
Here you can see the C Major Scale laid out and the notes of both chords underneath. You will notice that they are basically the same, they both have C, E and G notes (that makes up your C Major triad or what you may refer to as a normal C chord) plus a B note on top. With a C Major 7 chord the B note is left unchanged, with the C7 is becomes flattened.
So that’s it, just remember that when you see a 7 chord (A7, B7, D7, C7 etc.) then that actually means Dominant 7, which actually means Flattened 7th. Because Dominant is the ancient babylonian word for flattened, as in ‘my Babylonian cake came out of the oven as dominant as a pancake’*. If it is a Major7 chord then it will say, CMaj7, CMajor7, or sometimes a triangle (thats not a joke, look at some jazz sheets, Ctriangle7 means CMaj7) and you can leave the 7th note as is.
The Slightly Longer Answer
Firstly, this is about punctuation, try to think of it as C,7 or C,Major 7, this is obviously quite appalling grammar and you should never write the chords down like this but it demonstrates a point. The point being that the C is separate to the 7 or Major 7. If we were to give CMajor7 it’s full title then it should be:
C Major with a Major 7,
Or the even more detailed:
A C Major Triad with a Major 7th note added on top.
The 7th note of a Major scale is called the Major 7th, that’s pretty simple. So the Major Triad, which is the 1st, 3rd and 5th notes of a Major Scale played together with the Major 7th note added on top becomes a Major7 chord.
Similarly, a C7 chord should really be called:
C Major with a Dominant 7
A C Major Triad with a dominant 7th note on top.
What’s a dominant 7th?
Here is where the confusion lies. A C7 chord is not actually called a C7 chord, its full name is a C Dominant 7th chord, it’s just that writing that down on a chord sheet or above a line of music is a bit complicated to fit in. Occasionally, on a Jazz sheet you may see it written as Cdom7 but that is rare. The important thing to remember here is that C7, C Dominant 7 and Cdom7 are all the same chord.
The reason why a dominant 7th note is called what it is called is because it is the 7th note of a dominant scale.
Here is a C major scale:
C D E F G A B C
Here is a C Dominant scale:
C D E F G A Bb C
As you can see, the only note difference between the two scales is that 7th note, not flattened in the Major scale and flattened in the dominant scale.
The reason why the word dominant is used has to do with a dominant 7th chords relationship in Diatonic Harmony. In essence, the 5th chord of any Major Diatonic Harmony is a Dominant 7th Chord and if you play this at the end of a piece of music before playing the 1st chord of the diatonic harmony then it makes a really pleasant sound called a perfect cadence. So perfect this cadence is that the people who wrote down western musical theory all those years ago decided that it was so much better than all the other cadences that it dominated them. I may be working from knowledge I learnt twenty or more years ago but I think that is the crux of it.
Here is another little bit of knowledge for you, the Dominant Scale is also the Mixylodian mode. If this makes you panic and you are starting to break out in a sweat over the idea that to understand all this you need to learn all of your scales then do not worry, it’s not necessary, in fact in a lot of ways it’s a complete waste of time.
The only scale you really need to understand is a Major scale, from there you can easily work out everything you need to know, but that is another post for another time, what do we need to remember here is
C7 and CMaj7 are two different chords.
C7 means C dominant 7 and dominant means flattened 7th.
I hope this helps someone that needs help with this.