With modes, sometimes you need to step back to start to understand them. So let's go back to the basic understandings of a mode: a mode is simply a major scale - but with a different note as the tonic or home tone.
So the key of G has the notes: G,A,B,C,D,E,F#,G
A Dorian has the notes: A,B,C,D,E,F#,G,A
Same notes right?
Different order - THIS matters.
A Dorian has the note A - which also means that its associated chord (Amin) is the tonic or 'home tone'. So a song that uses the notes of the key of G - BUT IS CENTERED AROUND THE CHORD Amin is a Dorian piece.
Sounds simple yes? Well it is.
But here's the thing; YES - you can use all of the chords that live within the key of G. But the problem is, this pool of notes (or pitch collection) has a STRONG gravity towards the note G - NOT A. So the more of these chords you add to your progression, the less 'Dorian' it will sound.
This is why typically, most songs considered truly "modal" are based around just one or 2 chords. Using only one or two chords can create the sound of a drone of sorts. This harmonic simplicity allows the listener to soak in the true nuances of the desired mode. Think bagpipes or Indian music. A constant note provides a built-in framework, which has a real beauty to it.... or ugliness as desired.
Let's also discuss a couple other confusing things:
- The use of a 'scale mode' and something being 'modal' are not the same. During a solo, over a static chord, sure you can use different modes momentarily... Jazz guitarists do this all the time. But understand that this does nothing to affect the songs overall modality. The chords define the mode NOT the scale you are choosing to use.
- Modes are NOT scale shapes.... well, I mean, they are... or can be. But playing in Mixolydian mode (for example) can be fingered a number of different ways. Typically guitarists tend to think of things as fingering shapes - again TYPICALLY with the root centred on the low E string. This is not what is going on here. All the answers lie in the notes or pitch collection used.
You want to write a modal piece? It's simple.
STEP 1: Pick a mode
Let's pick Mixolydian, the fifth mode of G (for example). The V chord in any key is dominant, so that means to get the Mixolydian sound, we use a D7 chord as the root of our progression. So strum away and record yourself doing so... one chord, chug, chug, chug.
STEP 2: Write a melody (or 'head')
Play around until you find a melody that works over your D7 backing.
STEP 3: Support the newly created melody
Once you have your drone and melody in place start adding in chords (again, of the key of G) to your backing - but whatever you do, make sure you keep going back to the D7.
The key here is KEEPING IT SOUNDING LIKE D.
Voila! A modal song. This concept confused me for soooooo long that when i finally grasped it, it seemed anti-climactic. I hope that just happened for you too. : )
Modal understanding should be a part of every musicians bag of tricks. BUT - it is not some magic potion. Applying creativity to everything you do IS what it is all about. So armed with this knowledge, get out there and write me a classic. Modal sounds have been utilized by everybody from the classical masters, to the Beatles, right up to this day. You can learn to use them too.
With a little practice of course!