Here's a good old classic rock tune for today's lesson: Fortunate Son. It's got a great intro riff that will be instantly recognizable by anyone you play this for. Did I mention its also easy-peasy? Most of the riff is built on inverted third intervals (whew that's a mouthful!). What I mean by that is the root note is on the B string, and they're adding a third up from that root note (4 semitones), but dropping it an octave, thus inverting it (normally the lower note is the root, but in this case the lower is).
Take a look at the Em7 chord (barred, root on the 5th string - 7th fret) and ignore the bar part. That is the first formation in the riff, right? The notes that are being played are B (4th string, 9th fret) and G (2nd string, 8th fret). The root note is the G, and we're in the key of G. If you count up from G 4 semitones (G#, A, A#, B) you hit B. B is therefore a major third of G.
If you can figure out the theory behind this, you can start to see broader applications for the patterns that are being used in this riff (different keys, songs, etc). Let me know if you'd like to know more and maybe I'll do a whole lesson on this topic.
One other quick note. If you want to see the video larger, don't forget you can click the button in the bottom right corner of the video player for full screen. You can also click on the HD for high definition (much better quality picture and sound). Also, I've got other guitar songs lessons on the site too.
Watch the Fortunate Son Guitar Lesson:
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