Intervals: Fourths, Fifths & The Tri-Tone

Welcome back! It’s time to delve a little deeper into intervals. This week we’ll get into three of the most important intervals for hard-rock and metal: the fourth, the fifth and the tri-tone. Let’s start with a quick review. Remember that intervals are defined by their relation to the major scale. Here’s the A major scale and its intervals:

A major scale

A major scale

The fourth above A is D. The fifth above A is E. With me so far?

One of the things ancient musicians thought a lot about were the concepts of consonance and dissonance. In terms of intervals, consonance means notes that sound compatible with each other. The opposite, dissonance, means the notes fight each other. 

One isn’t better than the other, they’re just different sonic qualities. The two intervals we’ve looked at so far, octaves and unisons, are very consonant. Today we’ll look at three intervals with different levels of dissonance.

A Fifth of Rock and Roll

Where would rock and roll be without the fifth? Sounds so nerdy, but it’s true. The interval of the fifth is the building block of rock guitar. Before we get into the theory, let’s look at the shapes. These might look familiar:

Perfect fifth shapes (adjacent strings)

Perfect fifth shapes (adjacent strings)

If you haven’t yet guessed, the fifth is the basis of the power chord. The power chord, as we all know, is the lifeblood of rock. Two little notes jammed through a cranked-up Marshall can sound pretty special. Why do they sound so powerful?

The fifth is a particularly consonant interval. The notes vibrate together well, especially on an overdriven electric guitar. In fact, a distorted guitar amplifies the dissonance of any interval. Playing something that is dissonant with a clean tone is different beast when it’s played dirty.

The shapes above are the way most people play a fifth (particularly for power chords), but the shapes below are also handy to have in your head. They skip a string in between so the higher note (the fifth) occurs on a lower fret.

Perfect fifths (skipped strings)

Perfect fifths (skipped strings)

Holding Fourth

The fourth is nearly as consonant as the fifth. Remember that a consonant interval sounds “good” on a distorted guitar. I find fourths the easiest shape to remember. Other than the fourth pair, a fourth up is always on the same fret the next string over. Fourths look like this:

Perfect fourths (adjacent strings)

Perfect fourths (adjacent strings)

Fourths work well in rock, but they’re also a big part of jazz, especially when you “stack” several fourths up in a row. Put your amp on a clean setting, flip to the neck pickup and play this:

Many stacked fourths make jazz!

Many stacked fourths make jazz!

Jazzy, eh? Makes you want to put a black turtleneck on and punctuate your speaking with “daddy-o”, right?

The Devil’s Interval

The tri-tone (also called the “flat fifth” or “sharp fourth”) is an interval between the fourth and the fifth. If a fourth is 2½ steps and a fifth is 3½ steps, the tri-tone is three-steps (hence the name). Tri-tones look like this:

Tri-tone shapes

Tri-tone shapes

Now crank that amp back up and play this:

Feel the sinister power

Feel the sinister power

Sounds positively evil, doesn’t it? It turns out the Holy Roman Church thought so too and labeled this interval, “the devil’s interval”. With an endorsement like that, what self-respecting metal head is not going to play that interval?

The tri-tone above A is D♯. If you look back at our major scale chart, you’ll see that D♯ isn’t even one of the notes. That’s okay. Remember that intervals are named in relation to the notes of the major scale. That’s why we can also call this note a “sharp fourth” (because it’s one degree sharper than the fourth) or the “flat fifth” (because it’s one degree flatter than the fifth).

The tri-tone also makes it’s appearance in jazz and blues, but in a different form. Take a look at this A7 chord and notice the tri-tone interval in there. The tri-tone isn’t just for metal-heads.

The tri-tone in a 7th chord

The tri-tone in a 7th chord

Perfection, Augmentation & Dimunition

While we’re here, let me throw a couple of “muso nerd” terms at you. The fouths and fifths we looked at earlier are said to be “perfect”. It’s a weird word in this context because it doesn’t necessarily mean better. A perfect fourth is an interval matching the distance between the root and fourth degree of the major scale. A perfect fifth is an interval matching the distance between the root and fifth degree of the major scale. But, as we saw with the tri-tone, you can move a semi-tone in either direction. So what do we call those notes?

Any degree that is called “perfect” can be augmented by increasing the interval by a half-step (one fret). So the tri-tone could also be called an augmented fourth since it’s a half-step wider than a perfect fourth.

Going the other way, any “perfect” interval can be diminished by decreasing the interval by a half-step. So, again, the tri-tone could also be called a diminished fifth. More things to remember—just what you needed, right?

We covered a lot of ground today. Just remember that all we’re talking about is the distance between two notes and the shapes they make on the fretboard. It doesn’t matter if you play these notes at the same time, or one at a time. The interval is still the same. Getting these names, shapes and sounds down will help you as you dive further into chords, arpeggios and scales all of which will help you understand the music you’re playing and with your own improvising.

Until next time, keep rocking!