Originally Posted by: TheSquidOh man, I thought you had to stay in key to use modes, for instance the progression above thats in Gmaj. I thought you had to use the relative modes to the major, and play over the chord happening.[/quote]
You don't have to, but it is by far the best place to start. I always suggest to players to indentify the key and understand what modes belong to that scale expressed by the key signature.
[QUOTE=TheSquid]So really, you can use any key/mode as long as it has the three notes of the chord present in the scale?

Sure, why not? But it definitely helps to have a system for doing that also. So, learn to know the key and apply the modes of that key/scale. Then branch out and try other options one at a time. If one sounds good to you, remember it for future use. If one sounds bad to you, remember to avoid that one!

And I want to raise another point here. Sometimes I hear players (and especially people that imagine themselves to be :rolleyes: ) talk about their disdain for, or disinterest in "the rules". And you know what? Fine, you know? Hey, you can play anything you want.

But, let's get a few things absolutely straight.

1. The western musical system of diatonic/chromatic notes is an organized, integrated system.
2. This system conforms to the laws of acoustics (a subdivision of physics) and the physiology of the human ear, thanks to people with enough genius to discover those laws.
3. The only reason guitars (and other musical instruments) even exist and function is that people build them to conform to this organized, integrated system that is music.

Therefore, we are not talking about "arbitrary social conventions" invented by some dead, European white guys that were trying to "oppress us" by making us follow their "boring rules of music".

We are talking about a science that identifies certain laws of nature and makes use of them in a very specific, highly organized manner. :)

Ultimately, you can play anything you want. But only by approaching it from the conceptual perspective will you be able to understand how it all works. And eventually, to be able to identify what you hear regardless of whether it is in key or out; a "proper", consonant mode or a completely dissonant one relative to the chords you are playing over.

It is valuable to have a systematic method for mentally organizing the sounds that are possible into recognizable categories for future reference.