Interval Derivation For Dominants?

[wise]

Keeping it simple and using the major scale for example, my question is:

If you're dealing with the chord types for the degrees as follows:
I_____II____III___IV____V_____VI____VII
Major minor minor Major Major minor dim

Since the relationships between the root, 3rd, and 5th are in the form of a Major for degree V, how does the dominant chords fit in here? I recognize that the interval between the root and third is the same for both Major and dominant chords, but I guess my question is, how do you know which forms must be played in Major form and which in dominant form for that particular degree?

This knowledge is important to me because I am currently working on composing some solo work using the Lydian Mode.

Using my knowledge of intervals, the chord types would be:
I_____II____III___IV__V_____VI____VII
Major Major minor dim Major minor minor

This leads me to wonder if degrees I, II, or V should be using dominants instead of Major's? What's the missing link here related to dominants versus Major's? Thanks guys.

'Chris

[smfulla]

Sorry I couldn't help you man. I left school before they covered dominants =]]]
Shawn will help ya tho

[cyberfret]

A major chord has only 3 different note names. If you are looking at a G chord the notes are G B and D. A dominant 7 chord has 4 different notes. So a G7 would be G B D and F. So a major chord is part of every dominant 7th chord. The key to knowing whether you can use a dominant 7 chord in place of a plain major chord would be if the notes are within the key.

Here are the basic 7th chord for the key of C major.

I - Cmaj7
II - Dm7
III - Em7
IV - Fmaj7
V - G7
VI - Am7
VII -Bm7(b5)

There are definitely other chord possibilities that can be built from each degree of the scale. For a list of some of the possibilities check this page of the "major key harmony" lesson.

http://www.cyberfret.com/theory/major-key-harmony/page5.php

So if you were writing something in an F Lydian mode.....the relative Lydian of C major, you could use any of the chords listed. You just want to emphasis the F chord.

--Shawn