Originally Posted by: Fret spiderok i folow you so far. thanks for the reply

but what exactly makes certain chords 'tense', is it something to do with the intervals in them, or what.

and how do you switch between diatonic and other scales.

I'll answer your second question first. Take a really common chord progression like this:

Aminor/Gmajor/Fmajor/E7
repeat


The progression is in the key of Aminor. Notice how the 5th chord at the end is a dominant 7th rather than a minor chord. An E minor chord would have a 3rd of G, but the Dom7th chord has G# as it's 3rd. But look at the progression, there is a G chord in there which doesn't fit with the G#.
An easy way to play over this progression would be to play the A Aeolian (or pentatonic) minor over the A, G and F, but switch to the A harmonic minor (with the G#) for the E7 chord.

That was probably the simplest example I could think of, now let's get on to the subject of tension and release.
It's been long known for jazz players especially the the 2-5-1 and the minor 2-5-1 progressions are very satisfying and pleasant sounding progressions.
take the minor 2-5-1 that I showed you earlier:

Aminor7b5//D7//Gminor

notice how when you play the D7, you can sort of hear it 'wanting' to go to the Gminor, like you know it's coming. This is sort of what I mean by tension, a tense chord is a chord that 'wants' to go somewhere else. Take the Gminor chord now, the Gminor chord in that progression is quite happy where it is, you can't feel it wanting to go anywhere.

There are ways to make chords even more tense, so that the release is even more satisfying, here's another minor 2-5-1 in Cminor where I have changed the 5th chord even more to make it want to go to Cminor even more:

Dminor7b5//D7#5/Cminor

here's how to play it:

-------------------------------------------------------------
----6----------4--------4------------------------------------
----5----------4--------5------------------------------------
----6----------3--------5------------------------------------
----5----------x--------3------------------------------------
---------------3---------------------------------------------

can you notice the G chord wanting to go to the Cminor?

You see, this sort of theory does not fit in with modal theory and the major scale, it just fits in with what sounds good to the ear.