If you read and understood my column titled Understanding Chords, Part 1: Major and Minor Chords youre ready to learn about 7th chords and 9th chords. But if youre still a little foggy on those initial concepts, go back and read that column a couple more times. You'll get it.
So, picking up where we left off in Part 1, lets take a C major chord, which contains the notes C, E, and G, and turn it into a 7th chord. To do so, youll simply want to continue the alternating alphabet technique explained in Part 1. If C is the root note (the note you designated as number one) of the chord, E is the third, and G is the fifth, then, as you can probably see - by skipping the note A because A is the sixth of C - your seventh note will be B. The Musical Numbering System
By now you understand the alternating alphabet concept that is the basis of all chord building. That's simple stuff. Hopefully, you also understand the numbering concepts we've been discussing. That's even more important than the alphabet thing. In the previous examples we have only numbered the musical alphabet through one octave: C (one), D (two or second), E or E flat (major or minor third), F (fourth), G (five or fifth), A (six or sixth), B or B flat (major or dominant/flat/minor seventh), C (one again). But in naming notes or chords we actually use numbers up to thirteen, which requires that you number the notes through two octaves - or at least part way through two octaves. Common chord forms in almost all styles of music include chords with notes that would be referred to not only as thirds, fifths, and sevenths, but also as 9ths, 11ths, and 13ths too. Thats it though. In fact, no one ever says 8ths (the 8th is actually the octave of the one) or 12ths. And rarely do you ever hear anyone say 10ths (although I do hear that occasionally - the 10th is the same as the third one octave higher. Dont say 10ths though, say third). And no one ever refers to any notes as 14ths. And by the time you get to 15, youre really just talking about another octave of your one or root note. The musical numeric designation for certain notes changes in the second octave from what they were in the first octave. This isn't difficult stuff though, so dont freak out. Remember, youre still only spelling to G and counting to 13. Easy. So here is the C major scale numbered through two octaves, with the most common numerical designations applied to each note:
In the system of musical numbering, a one is always a one, a third is always a third, a fifth is always a fifth, a seventh is always a seventh. The second changes to the ninth in the second octave and above. The fourth changes to the eleventh in the second octave and above. The sixth changes to the thirteenth in the second octave and above. That's it.
How Music is Numbered
Remember how we designated C as one, and gave the rest of the musical alphabet corresponding numbers? Thats a key concept to understanding all of music. And its easy - there are only seven letters to remember. Read this sidebar, and then work on this whole thing using other notes as one, instead of C. For example, figure out what number B is when you use E as your one. Youve heard the musical phrase one-four-five chord progression. This numbering concept is what that is all about. It's essential musical knowledge. Read all about it here.
Anyway, using that simplified view of music, and not yet worrying about sharps and flats, a C7th chord contains the notes C, E, G, and B. Simple enough, right? This is easy stuff, although there is a catch. But, no worries, thats easy too.
Dominant and Minor 7th Chords
As you learned in Understanding Chords, Part 1, there are two kinds of thirds (major and minor, which are one fret apart from each other in any chord, or in any scale - see the sidebar titled Minor Chords in Understanding Chords, Part 1 to learn more about this). There are also two kinds of seventh note, which end up making various kinds of 7th chords.
The most commonly used 7th chords are what are known as dominant 7th chords, which include a dominant, flat, or minor seventh note (all three are the same thing; flat seventh is the most common way to refer to this note while dominant 7th is the most common way to refer to the chord it builds). This type of seventh note is found two frets below the root note, so for a C chord, the flat seventh is the note B flat.
You can add that flat seventh note on top of either a major or minor chord. Continuing to use C as our basic chord, if you build the chord C-E-G-B flat, you have built what is called a C dominant 7th chord. This is easily the most commonly used 7th chord of all, so using the formula 1-3-5-flat 7, learn how to build a dominant 7th chord for every major chord you know. (Spell them out using other letters of the musical alphabet as your one, then figure out how to play them on the guitar.)
Heres one dominant 7th chord shape to get you started:
If you use the C minor chord instead of the C major chord, constructing your chord C-E flat-G-B flat (the formula would be 1-flat 3-5-flat 7) youve built what is called a C minor 7th chord. The minor 7th chord form is the second most commonly used type of 7th chord, so again, learn to build minor 7th chords out of every minor chord you know.
Heres one easy minor 7th chord:
Major 7th Chords
I told you there are two different types of seventh note. We've already discussed the dominant or flat seventh. Now let's cover the major seventh. The note that is known as the major seventh is only one fret beneath your root note, as opposed to two frets as in the flat seventh. So when building a C major 7th chord, youll use the note B instead of B flat as your seventh, building a chord spelled C-E-G-B. This is a very melodic sounding chord that is often described as a jazz chord, but it's uses go far beyond jazz. It's a cool chord to know, even though you wont be using it as often as a dominant 7th or minor 7th chord.
Heres one type of major 7th chord:
And, though the name might cause some confusion, don't be fooled into thinking that a major seventh note can only be used on top of a major chord. You can throw a major seventh note on top of a minor chord too. Try playing a chord using the notes C-E flat-G-B. This is called a minor-major 7th chord. Youre less likely to encounter this chord anywhere - but then maybe thats exactly why you should learn it and put it to work, so you'll come up with a sound that most other musicians aren't using, and you'll make a name for yourself and gain a reputation as an innovator.
Building 9th Chords
You've probably got the hang of this now. To build a 9th chord, youll simply take the alternating alphabet technique one step further, skipping the note that comes after the seventh to add the ninth note of the scale. So for a C9 chord, the ninth is D.
Just like the 7th chords, of course, there are both major and minor 9th chords. And for the most common form of 9th chords, the chord will include a flat seventh. The formula for a 9th chord is 1-3-5-flat 7-9; the formula for a minor 9th chord is 1-flat 3-5-flat 7-9.
With that in mind, here is a C9 chord:
And here is a C minor 9 chord:
You can, of course, build a 9th chord that includes a major seventh instead of a flat seventh. That chord is called a major 9th chord (as opposed to the more typical 9th chord, shown above). The formula for this chord is 1-3-5-7-9. Ill show you two great C major 9 chords, one of which leaves out the third (Diagram 7a), and the other which leaves out the fifth (Diagram 7b). That's OK though. I'll talk about leaving notes out a little later.
Two types of major 9th chord: [Diagram 7a: a C major 9 chord with no third]
[Diagram 7b: a C major 9 chord with no fifth]
You can also build a 9th chord, with a major seventh, over a minor chord. The formula for that chord is 1-flat 3-5-7-9. I'm showing you a variation on the chord diagrammed in 7b, which has a root note, third, 7th, and 9th, but no fifth. In this case the third now become a flat third, which is what makes the chord minor.
One type of minor 9th major 7th chord: [Diagram 8: a C minor 9 major 7 chord]
Leaving Notes Out
As you've seen above, you can build chords that dont even have all the chord tones. You can even build any of these 9th chords without the seventh, without the third, without the fifth - even without the root note. And that leads to another opportunity - and dont think of all this as the mind-boggling mess it might seem, think of it all as massive opportunity for variety in your playing.
In any chord that goes beyond 1-3-5 or 1-flat 3-5, you are free to drop notes from the chord, either to make the fingering easier, or to play a more distinctive sounding chord. I'll just give one more example, and leave the rest to your imagination, exploration, and discovery.
Let's use a regular 9th chord for this example. The formula for a 9th chord is 1-3-5-flat 7-9. Using C as our demonstration chord, that means C-E-G-B flat-D. But you don't actually have to play all these notes to play the C9 chord.
Here is a very common C9 chord form - especially in blues music - that contains only four notes, actually leaving out the root note, C. The chord still works though, because the sound of it clearly implies the intent of the chord. Even without the root note, this is clearly a C9 chord. Officially, it would be called a C9/E, because it is a C9 chord with an E in the bass:
As I said before, you can leave almost any note you want (obviously, if you leave out the 9th, its no longer a 9th chord). It's not always the root note youll want to leave out. Most often, its the fifth of the chord. You'll almost always want to keep the third, because of its key role in determining whether a chord is major or minor. And if youre working on a 7th chord, youll of course want to keep the seventh in there; if you're working on a 9th chord, you'll keep the ninth, throwing out either the root, fifth, or seventh.
I'll stop filling your brain with detours here and let you wander off to either try all these things on your own or go bang your head on the wall. The choice is yours. Have fun.