A few questions about chord theory

Got a few questions about chord theory. First one...how do you get a dominant 7th chord. Second, are chord progressions only in a key, or can they be in a key/mode (I'm assuming it's key/mode seeing as how there are minor keys...unless this the only exception.) Also...I'm having a tough time wrapping my mind around what the difference is between being in a major key or it's relative minor(I know that it sounds different with the minor key being somewhat more sombre) but it's the same notes...is it just a question of thinking of it as a flatted 3rd 6th and 7th and playing it accordingly like in soloing? :? Responses are appreciated, thanks.

First off, a dominant 7th chord is a 7th chord that is placed on the 5th note on the major scale, it's the same as a major 7th chord with a flattened 7th. In theory, each note has a name, the fifth note of C for example is G, so G7 is the dominant 7th of the scale, it has the notes G, B, D, F. G major would be G B D F#. Second, chord progressions are generally in minor or major keys, I was told that a mode is purely melodic so technically speaking a chord progression is different then a mode, however chord progressions don't have to follow a key completely, it can have outside chords and notes, this is the basis of harmony. Major keys and relative minor keys do have the same notes, the only difference is that you start on different notes: A C major key should resolve/start on C, An A minor key resolves/starts on A, even though they contain the same notes.

You take a major triad and add a minor 7th to it.

Hey, where are all the smileys?

All the stuff above looks right.

The big difference between major/minor in progressions is the V chord. A dominant seventh really wants to resolve down a fifth, so V7-I or V7-i are very strong - they're called authentic cadences.

If you harmonize a scale in four notes, the major scale gives you that dominant chord on V, for V7-Imaj7. The minor scale doesn't - you get a minor seventh to a minor seventh. It's an OK change, but not as strong as the authentic cadence.

About 4-500 years ago, composers realized that by raising the seventh note of the minor scale they could get the V7-i change. That's why we have the harmonic minor scale... it harmonizes to give us the cadence our ears want.

So the difference for progressions is: C major will almost always have C, F, and G7... A minor will almost always have Am, Dm, and E7. The E7 isn't 'in key', but it works because of the harmonic minor scale.

You will also find a lot of dominant 7th chords in Jazz/blues stuff on chords other than the V. Here, it's done to reduce dissonance.

In a blues progression done in a jazz style with a few substitutions, it's not uncommon to see runs like:

II7 | bVdim | I7 bVII7| VII7 VI7 | II7 etc.

What's happening here looks insane from a theory perspective, but it works. Keeping everything Major keeps it bright and happy, adding in the b7 to every chord reduces the dissonance between the changes, and everyone just gets along.

In blues, I guess you could look at using all dominants as reducing dissonance between the chords - but the chords will all have the tension typical of dominants. You're maintaining the tension, and delaying the release. What that really does is support the dissonance created between the chords and the melody.

Since the blues scale has both a b3 and a b7, there's always a bit of a dominant sound to the melody lines. Using chords with the b7 instead of a natural 7 lessens that dissonance a bit, since the melody b7s will now blend in with the chords.

When you do use dominants throughout a blues progression, it's typical to use a major type chord at the very end - not as part of the turnaround, but as the last chord played in the song. Some folks use a simple major, others (like me) prefer a 6/9 for a more 'jangly' type sound to the finish. A few even go the other way, and use an ending chord that's an altered dominant, to increase the disonnance even more and let it just hang in the air.

I do like to finish up blues with a 9 chord. I probably overdo it. :D

I like the I6 chord myself . . . but I'll do a 6/9 on occassion :)