Quote Originally Posted by tugboat View Post
The entire first minute of the song seems to be in E major. But at one point during this part he plays 2 - 2# - 3 (or 2 - 3b - 3). Then it jumps to the A string and the riff repeats.
The whole song is in E major. However, he is not using the major scale. He is using a combination of major and minor pentatonic scales. The reason that it sounds so major is the emphasis on the major 3rd in the signature melody. But listen closely, and you will hear hammer-on 3rd's and flattened 7's, especially toward the end of the first minute. The accompaniment is also filled with flattened 7's right from the start.

If it had a true E major feel to it, you would hear the 7th degree of the major scale a lot more prominently, especially at the V-I cadence. The fact that it is not there in any distinct way puts the melody a lot more toward the major pentatonic.

But this is way too much analysis for a simple blues like this which was played largely intuitively and not derived consciously from any theory of harmony.

Even that last paragraph saying we are being too analytic is too analytic.