Watch the Theory, Scales & Colors online guitar lesson by Steve Vai from Alien Guitar Secrets: Passion & Warfare
Now let's talk briefly about scales. Most of you already know what scales are: just a series of notes. There's a lot to say about scales and the theory behind them, but let's just talk a little bit about the music theory here. I get asked a lot: "How do you feel about music theory versus playing from the heart?", which is one of the stupidest questions I can ever get asked. It's like saying if you have one you can't have the other. You can have either of them in any degree, it's just based on what you want to do.
So, in the realm of developing your understanding of scales and music theory, the rule of thumb is that if you're interested, nothing will stop you from understanding it. If you're uninterested, nothing will help you retain it. And if you're not interested, don't worry about it - you don't need to know one bit to be an effective, incredible musician. But you do have to have a good ear, which takes a tremendous amount of developing.
Personally when it came to music theory, I wanted to know everything about it. I thought little black dots looked like art. I wanted to know how to write music and have total command over it, because instinctively I knew that the process of composing was infinite. I especially love composing orchestral scores - I love thinking about it, visualizing it, and then manifesting it, and suddenly there it is being performed. Incredible. But, you don't have to understand music if you don't want to and can still be very effective.
Back to the technique - I could show you scales and explain them, but you can get that information someplace else. I'll say that scales are like colors; when learning them, practice them from lowest to highest and then backwards (and if you make a mistake, start over from the beginning), and eventually what becomes important is the color or flavor of them. And with modes, besides learning the fingering and theory behind them, memorize the color of it. Again, you can learn them, but you don't have to. I like knowing all the scales that I can, but more than that I like understanding the flavor of the scales. When practicing, that's what you listen for.