Overall Rating: 4.7 (of 5)
Classic Double Stops: 3rds & 6ths
Before we get into some cool double stop licks using 3rds and 6ths let's get some definitions out of the way. A double stop is just guitar lingo for a "harmonic interval", or more simply, two notes played together. Unlike chords, which are generally made up of three or more notes, double-stops are composed of only two notes (hence the word "double"). We call the distance between these two notes an interval.
In popular music, for these intervals to sound correct in the key you are playing, they must be diatonic. That's just more guitar lingo meaning that both of the notes in the double stop must be within the key - or more simply "from the same major scale".
If this is confusing just take a look at a C major scale. If the root note C is the "one" of the scale, then D is the "2nd", E is the "3rd", F is the "4th", G is the "5th", A is the "6th", B is the "7th", and C is the "octave". By simply applying this numbering system to each scale tone, and taking into account the quality of the relationship (major or minor) you will be able to determine the nature of the intervals for any scale. Therefore E is the "diatonic" 3rd, or major third of C.
Now take a look at the sequence below. Here are Major 3rds in the key of C. As you play along try to notice the repetitive patterns that your fretting fingers follow.