Parallel fifths and their inversion, parallel fourths (think “Smoke on the Water”), are usually a little easier for beginners to play than parallel thirds, but they not only can sound muddy, they’re a traditional-harmony no-no. (They may even result in a knuckle lashing if played within earshot of some music professors.) Parallel thirds, however, have an open, inviting sound and are found in every genre, from jazz to classical to gospel to metal.

To get started with thirds, play the single-note G major melody in Example 1. Now, let’s put on our “3-D glasses” and, as demonstrated in Ex. 2, transform the one-dimensional theme by harmonizing each note with a major or minor third as dictated by the parent scale, G major. With these shapes under your fingers, you’re now in command of grips that power one of the catchiest guitar hooks in rock and roll history—the intro to Van Morrison’s Summer of Love smash “Brown Eyed Girl.”

In the mid-’70s, Fleetwood Mac’s Lindsey Buckingham took over as pop-rock’s undisputed champion of parallel thirds when he tracked the guitar part on “Rhiannon.” A moody, syncopated A min or hook similar to Ex. 3, “Rhiannon” is a tad trickier to finger than “Brown-Eyed Girl” because it adds a simple bass line on the two lowest strings. (Tip: thumb the bass part and pluck the thirds with your index and middle fingers. Or, play the lick “hybrid”-style, picking the low notes and plucking the thirds with the middle and ring fingers.)

Thirds are great fun loud, too, as AC/DC’s Angus and Malcolm Young proved so well with the main theme to “Rock and Roll Ain’t Noise Pollution,” the first single from the 1980 hard rock benchmark Back In Black. On this track, the Young brothers got a massive sound by playing thirds similar to Ex. 4 through tandem half-overdriven Marshall rigs, and room mics added even more power to the sound. But, expensive studio gear aside, no matter how you sing, play, pick, pluck, or track thirds, they’ll always be a cheap and easy way to make a melody come alive.