Hey guys.

Could someone please tell me why some chords have numbers after them (G7, C5 etc.)

I know it is obviously because it is their name, but why is the number what it is? What makes a note a 7th or whatever.

Thanks in advance for any explination
Hey, to be honest I don't know that much about it myself, but I do know this much:

5th chords are just another name for power chords, I think the 5th part has something to do with the fact that playing a note on the 5th fret is the same note of the next string up if played open.

I know even less about 7ths, but basically it gives the chord a different sound by changing one or two of the notes in it. That's about all I know, hope I've helped.
A Pirate's Life for Me.....
they have the numbers because of the intervals in the chord. so a C5 has the fifth of C in it. so the 2 notes in the C5 power chord are C and G. hope it helps?
“Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are part of nature and therefore part of the mystery that we are trying to solve.”

-Max Planck

ok, basically, the number refers to the number of the added note in the scale.

So, for C major the scale looks like this;

1 2 3 4 5 6 7 8/1

a normal "C" chord takes the 1st, 3rd and 5th of this scale;

in this case, that's C, E and G

when it says C7, it means that the 7th is added.

so this means its C, E, G and B, right?

no! This is where it gets complicated!

the added 7th will always be a minor 7th (dont ask why-its just is)

this means it will be the 7th note in C minor, not C major.

This is a semitone lower-b flat.

so the C7 chord is;

C, E, G, and Bb.
1 3 5 minor7

confusiing no??
The numbers after each of the chords are the numbers of the degrees in the scale. The note that is that degree is added to the chord.

For example, a C major scale (in notes): C _ D _ E _ F _ G _ A _ B _ C
Each of the notes are a certain interval in the scale, so:
C = 1
D = 2
E = 3
F = 4
G = 5
A = 6
B = 7
C = 1 (or 8, or octave, doesn't matter too much)

So, a C major chord takes the 1st, 3rd and 5th degrees of the scale, to give you: C _ E _ G.
A C major 7 (CM7) takes the major chord and adds the major 7th to it, in this case the B. So a CM7 gives you C _ E _ G _ B.
If it is just a C7 chord, it means to play the C major chord, but add a diminished 7th to the chord. To diminish a note means to flatten it by a semitone. So by flattening the 7th (B) you get a B flat (Bb). So a C7 chord is C _ E _ G _ Bb.
A Cm chord means to play flatten the third, so the chord is C _ Eb _ G. To play a Cm7 chord, you play the Cm chord, but add the diminshed (or in this case, the minor) 7th to is, so it gives you C _ Eb _ G _ Bb.

So, a C5 chord means to play the root (in this case, C) and the 5th of the scale, in this case a G. So your C5 chord = C _ G.

Hope that helps.
like someevildude said:

Every chord is built from a major scale. The major scale is built from a series of Whole and Semi steps (Whole and semi tones).

The series is this:

Where R = Root note
W = Whole Step
H = Half step.

If you put a note under R, and work on, you can get the major scale of any Note:

R  W  W  H  W  W  W  H
C  D  E  F  G  A  B  C  <-- C Major scale
E  F# G# A  B  C# D# E  <-- E Major scale

Like i said before, each chord is built from one of these scales.
So if its a C Major chord, you would use the C Major scale.
If its a G Minor chord, you would use the G Major scale.
If it was a Asus4/Eb chord, you would use the A Major scale.

The first note in a chords name is always the root note.

The next thing.
There are 6 basic triads:

And each one has intervals.
An interval is a number for each note in the major scale.
So, the first note in a major scale has the interval 1
the second note in the major scale has the interval 2
the 7th note in the major scale has the interval 7
and so on.

These are the intervals for each triad:
Major - 1 3 5
Minor - 1 b3 5
Augmented - 1 3 #5
Diminished - 1 b3 b5
sus2 - 1 2 5
sus4 - 1 4 5

now, your chord, A5 isnt a chord. Its a powerchord, or harmonic interval.
A powerchor only uses 2 intervals: 1 and 5.
A chord is 3 or more different tones.

A powerchord is 1 and 5, so if you apply that to the C Major scale, you get the notes C and G.

Therefore, these two notes, C and G make up the chord C5.
Been away, am back
im pretty sure there is a fuller sounding diminished chord, correct me if i'm wrong:
1, b3, b5, 6, for C it would be C, D#, F#, A right?
- tommy
Quote by tombomb22
im pretty sure there is a fuller sounding diminished chord, correct me if i'm wrong:
1, b3, b5, 6, for C it would be C, D#, F#, A right?

Eb and Gb not D# and F#. While they're the same note enharmonically, they're technically different.
Besides, how can you flatten the third and fifth to get the sharpened second and fourth?

I'm pretty sure that would be dim+6 chord too. The diminished chord would just be: 1, b3, b5, so C _ Eb _ Gb.