7th chords

You can use seventh chords anywhere. Blues and rock are full of them and it's one of the reasons that the minor pentatonic is the scale of choice for many guitarists, as it contains the b7 (the b3, as well, which often serves as a "blue note").

When sevenths are used, quite often you will find them serving as a "temporary fifth" for the chord change coming up. For instance, if you're in the key of C and happen upon an A7 chord, the chances are very likely that the next chord will be either D or Dm, both of which the A7 is the fifth of. In many theory books, you'll see a C - A7 - Dm progression written out as "I - V7 of ii - ii."

This is also why people make a big deal about the circle of fifths, because when you come upon one of these seventh chords, you can bet better than even money that it's going to be the fifth of the next chord in the progression. Again, using the key of C as an example, you might run into a string of fifths, like this:

C - E7 - A7 - D7 - G7 - C

The main thing to keep in mind is that every chord has different roles in different keys and that songs often involve moments of modulating between various keys. This is why (yet again using the key of C as an example) you'll often go from C to C7 and then to F, for the very reasons you mention, that you're turning the "V" of F (the same C that's the tonic in C major) into a "V7" chord.

As far as options in choosing scales for leads, the important thing to think of is just how long you're going to be in your "temporary key." Many of these changes of sevenths take place very quickly, so there's not always a reason to change your entire scale just for the duration of a beat or two. Best to look at the whole of a phrase, where it starts and where it rests, to decide what to do.

We'll be covering this sort of thing in our "Turning Scales into Solos" series - right after a brief discussion of the blues scale, which I believe will be online next week.

Hope this helps.

Peace

fantastic. thanks David.

I would like to add that the obvious scale of choice to play over a dominant 7 chord isn't a minor pentatonic but a mixolydian scale, a major scale with a flat 7. That's because a dominant 7 chord consists of the notes 1 3 5 b7. Playing a minor 3rd over it will sometimes sound weird.

Other things to think of is; are they functioning dominant? A functioning dominant is a dominant that resolves to a 1 chord. For example, let's say that we are in C major. If the chords are C F G7 C, the G7 resolves to it's 1 chord so it's a functioning dominant. Over a functioning dominant you can play either mixolydian or the altered scale. However, if you have like a progression of C D7 F G C or whatever, the D7 doesn't resolve to the 1 so it's a nonfunctioning dominant. Over this chord you can play a Lydian B7 instead (a lydian scale with a b7) and it will sound cool.

Over every dominant chord, functioning or non functioning, your first choice should always be to play mixolydian though.

Dominant 7ths don't really resolve to anything. You can almost toss them around in much the same way that one uses power chords.

To see what I mean, try this:

play a G7 using this fingering:

3 x 3 4 x x
G x F B x x

Now, move that around, walk down to C7 or up to F7, you'll find that it sounds fine no matter what you do.

You can play with minor 7ths the same way:

3 x 3 3 x x
G x F Bb x x

As for scales to use over 7th chords -- Just you have all kinds of options!

if you're in a minor key and the 7th is functioning as a V, then using the harmonic minor sounds fantastic, but you have to be judicious, this one is easily over-done.

You can use the HW diminished scale.

Mixo mode.

Major or minor pentatonic (depending on if it's a major or minor key center).

Lydian Dominant.

Altered -- this is tough to master, but it can really add some punch.

And really so many more.

Well, there's two kinds of dominant chords, functioning and non functioning. Some of them resolve and some don't. The classic usage is that they do resolve, like a G7 to a C, but thanks to blues and other kinds of music they don't always do this. The reason they usually resolve (especially in classical music and standard pop) is because the sound of a dominant chord is driving. There's a tritone interval and the b7 wants to go to a third. The dominant chord was traditionally used as a tension/release tool.

There's even a story of a famous conductor (forget his name) who had his maid come in and play a G7 on the piano in the morning, and he had to run up and resolve it to a C, and then he was awake! :D

7ths cords add creativity to a melody

the pedant in me (or maybe just the ex-philos student, same thing) is desperate to point out that it doesn't beg the question at all, it merely raises the question. sorry, I can't help it.

and +1 on KP's post - some dom 7ths act as functioning dom 7ths and resolve to the I chord (or tonic), but often in jazz or bluesy tunes, you'll come across lots of dom 7ths where they don't seem to resolve in this way at all. I tend to look at them and think "major chord in a jazzy tune", but I know Joe Pass considered them a unique category due to the distinct soloing possibilities available when playing over them. Alas, I've yet to reach Joe Pass's improvisational standards, so this knowledge has yet to serve me quite as well it has him.