Here's a fun way to apply some thirds in a blues style format over an E7 chord.
There are two types of thirds: major and minor. The major third is four semitones, and a minor third is three semitones. On your guitar, if you play a G on the 3rd fret, 6th string, at the same time as a B on the 2nd fret of the 5th string, you get a major third. That kiddy-corner pattern you get will produce a major third anywhere in the lower four strings.
To get a minor third, simply drop the B to a Bb. That same pattern will give you a minor third anywhere on the lower four strings.
The "progression" we're playing over here is actually just one chord - E dominant 7. I like playing it with the added D on the 3rd fret, 2nd string. The D is the flatted 7 (b7) that makes this chord sound so cool. Remember, E7 is neither major nor minor, and as such it can stand in like a body double for either one. In this particular case we're treating it like a minor chord.
When you're using thirds, think about what chords are in the key. If your I IV V chords are major, then the related thirds are going to be major as well. For instance, in the key of G, we have D major. Thus, when you're looking for a third to play off a D, play the major third.
If you're looking for a great way to apply the riff you learn in this lesson, I recommend working it over while playing along with these blues jam tracks. (There's a free sample track available at that link)
Alrighty - ready to dig into this? Let's get started.
Watch on Youtube