Basic Theory Question - why "9" and not "2"? (Page 1 of 2)

I've often wondered that too!
It's because it follows the following pattern:
Start at the root and by adding 3 and 5 you get the main triad.
Next add 7 to get your 7th (major or diminished)
Next comes 9.
It's just the sequence of adding 3rds above root note.
It indicates (reminds) that the 9th is usually played above the 7th (if present) and in a higher octave as you guessed correctly.
More here
http://juliewaters.com/chordtheory.php

Thanks guys.  I think I understand.

However, Jerome, I'm hoping you made a typo, otherwise you're going to have to explain a bit further:

>>"2 (and 4) are usually tied in with "sus" or "suspended" chords.  That is, you substitute the 2 for the 3, or the 2 for the 4.   As such, you need to stay within the octave."<<

Did you mean to say:  "you substitute the 2 for the 3, or the 4 for the 3"?

If you meant to say that, then I get it.  If not, then how about using D, Dsus2 and Dsus4 to explain what you mean.

Brings to mind a second question:  What is the difference between a sus2 and an add2?

Thanks.

Yup, that's what I meant to say. 

The difference between a sus and an add is exactly that.  With the sus, you suspend the 3rd.   With the add, you play the 3rd, and just add the 2 to the chord.

A 9 chord has a 7 in it. 1-3-5-b7-9 or maj9 = 1-3-5-7-9

or m9 = 1-b3-5-b7-9

A sus2 chord does not it's 1-2-5

A suspended chord suspends the 3rd usually a short chord.

Alan Parsons song Eye in the Sky uses the Dsus2 to D.
A first position D chord with an open 1st string.

A sus2 and a sus4 are the same chord with a different root.

Sus2 1-2-5 =C-D-G

Sus4 =1-4-5 = G-C-D

A Csus2 = G sus4

Bob1950

Totally alright.  More is better!

And your observation on the sus2 being an inversion of the sus4 is a good one.

Hi all...

would you like to help me>
I have a problem to meaning a cord.
What is A4?
I find it in dream theater-spirit caries on song TABS at ...

Thanks very much for to help me.

Stonebridge,
Thanks for your reply.
This part of it, "The minor 7th is also often called a dominant 7th because it leads back to the basic key.
e.g. D7 (D chord with a C in it) is often the chord that leads back to the key of G." is very helpful in telling me my C7 in question(with the Bb note) is leading back to the key of F(with primary chords of F, Bb, and C)
Also due to the fact that the B is flatted in the key of F.

You explain that my D reference is because I'm playing in key of G(with primary chords of G, C, and D)

My theory knowledge is limited, so I thank you for your help.

Please correct me if what I wrote is incorrect.

When we talk about "7" chords, we really mean "dominant 7ths" as opposed to "major 7ths."  And a dominant 7 flattens the 7, wheras a maj7 doesn't.

So a Cdom7 (C7) is C E G Bb, and a Cmaj7 is C E G B.

Ddom7 would be D F# A C, and a Dmaj7 would be D F# A C#.

In both cases the dominant 7 has a flattened 7th, while the major 7 has the unaltered 7.

Make sense?

It does make a differance on the piano, which gives a lot more options w/ 88 keys

Quoted for truth.  If you have access to a keyboard, it is much, much easier to visualize the intervals there than on a fretboard.

There is a logical reason for this. Sit tight, it may take a while...

The notes of the 8 note scale we all know (CDEFGAB and back to C) have been given names that express where they are in relation to the "tonic". These are
1. Tonic
2. Supertonic (above the tonic)
3. Mediant (middle note of the triad 1.3.5)
4. Subdominant (below, or lower,  dominant)
5. Dominant (most important note of the scale after the tonic)
6. Submediant (lower mediant)
7. Leading note (leads back to the tonic)
8. Tonic (or octave)

The 7th chord built on the 5th note of the scale, called the dominant note, is called a dominant 7th.
(It would be GBDF in the key of C.)
In other words, it's "dominant" not because it's a 7th, but because it's built on the dominant note of the scale.
Strictly speaking, a 7th should only be called a "dominant" 7th when it is, for example, G7 in the key of C. [G being the 5th note in the key of C]
This dominant 7th is important because it is the chord that often leads back to the tonic (base) key.
Over the years, any "minor" 7th has come to be called a dominant 7th because it has the same structure.
So, minor refers to the actual notes in the chord, the structure; but dominant refers to the original idea of this chord being based on the 5th (dominant) note of the scale, and being the most important 7th chord in that key.

I hope it has put your mind at rest

It's the consequence of the way chords are named.
There are major and minor chords in the same way as there are major and minor keys. In the key of C minor the root chord is the chord of C minor. C Eb G C. In C major it is C E G C.
Normally, the major chord is just written C, whereas the minor chord is written Cm.
If I add a 7th to the chord of C major, I have 2 choices, either the normal (leading note) 7th, which is a B; or the flattened 7th which is a Bb.
In music theory, the B forms a major 7th and the Bb forms what is called a "minor" 7th. Both these are in the key of C major.
Minor 7th here refers to the interval between the tonic C and the 7th. It doesn't mean that the chord is C minor. This is where it gets confusing.
So C E G B is C major, with added major 7th, to give its full title
C E G Bb is C major, with added minor 7th
The 1st usually gets shortened to C7 and the second usually to Cmaj7
Both of these short forms leave out a lot of information and are used because it's convenient and we all understand what they mean.

If you are in the key of C minor it gets even more complicated
If you add a 7th you can get
C Eb G B which is C minor with added major 7th **
C Eb G Bb which is C minor with added minor 7th
You can see the potential for confusion now!
If I say "C minor 7th" do I mean C minor with a major 7th or C minor with a minor 7th or C major with a minor 7th?
The answer is that this naming system for chords is not an exact science and has been simplified to make it easier to use.
There are conventions which guitarists follow where we all usually agree what, for example, C7 actually means.
The use of tabs makes things clearer. Then we know exactly what chord is intended.

To answer your question, the author is sort of right. It is what is usually meant by people when they use the expression.
A "minor" 7th can, strictly speaking, refer to the fact that the chord is minor, and also that the 7th is flattened.
To get around this, the term dominant 7th is used to indicate the case where the chord is major and the 7th is flattened.
As I said, in a major key, it's only the 7th chord on the 5th note of the scale (the dominant) that is naturally major with a flattened 7th.
This is why major chords with a flattened (=minor) 7th have come to be called dominant 7ths.
However, the 7th in this chord, because it is flattened, is called a minor 7th. This distinguishes it from the case where the 7th is not flattened, and is called a major 7th.
So, 7ths can be major or minor, and chords can be major or minor.
The author is, I assume, attempting to simplify this. When he says minor 7th, he is referring to a minor chord with a 7th. When he means major chord with a seventh, he uses the term dominant 7th.
It is confusing. Guitar chord names, in order to be useable, don't tell the whole story; and that's where the confusion lies.

I spent years studying music theory (piano) before I picked up a guitar. I found the naming of guitar chords very confusing initially because of just this way of simplifying the names of the chords.
I hope I've explained this reasonably well, but I may well have just made it more confusing!

** C minor with an added major 7th [C Eb G B] or any similar chord in another key sounds very strange. I can't say I know of any song which has this chord.