Alternating Thirds
Another important sound commonly used in Rock and all its related styles is the use of both the minor and major third of a chord. There are literally thousands of sax, guitar and keyboard riffs which either alternate between the two thirds or begin on the minor third and then move to the major third.
Here is an example of this sound in the key of A. The minor (or flattened) 3rd is C and the major 3rd is C#. The notes of this solo come from a combination of the Blues scale (which contains the minor 3rd) and the A7 arpeggio (which contains the major 3rd).
Here are some more examples which use both the minor and major 3rd of a chord. Once again, these riffs are making use of a combination of 7th arpeggios and Blues scales.
This one is another R&B style solo. Notice how the use of both of the 3rds makes it sound bluesy. The dominant 7th chord, combined with the use of the minor 3rd is the real heart of Blues harmony.
