In music, an interval is just the space between two notes, usually relating back to the difference in relation to a major scale. So, for example, the interval of a 3rd is four semitone (4 frets). The interval of a 4th is 5 semitones (5 frets) because a major scale, starting at the root (1) goes tone, tone, semitone..

Knowing how to quickly find and play 4ths (and any interval for that matter) is important for general note finding on guitar, improvising, and also building alternative guitar chords.

What Is A 4th?

As mentioned, a 4th is (generally) a difference of 5 semitone (or 5 frets) between two notes. So it’s the difference between the 1st and 4th degrees of a scale, but can occur in any interval that’s 5 semitones.

4ths don’t come in major and minor varieties like 3rds, but can be diminished (4 semitones) and augmented (6 semitones). Here you’re probably wondering what the difference between a major 3rd and a diminished 4th is, since they’re both 4 semitones. Or an augmented 4th and a diminished 5th, since they’re both 6 semitones. The difference is context. Going any further than that goes a bit too deep for a simple article about basic intervals, so I’ll leave it there.

What Does A 4th Sound Like?

The first two notes of the Bridal Chorus, more often know as Here Comes the Bride by Wagner are perfect 4th. It’s easy enough to hear what a 4th sounds like if you hum the song to yourself.

Playing 4ths On The Same String

As mentioned, the interval of a 4th is 5 frets. It’s a bit of a stretch to play on a single string, but certainly doable.

Single String 4th On Guitar

Guitar fretboard diagram showing the interval of a fourth on a single string.

This interval is the same for every guitar string.

Finding 4ths Across Guitar Strings

4ths are quite easy to find across the guitar strings because most of the strings are tuned a 4th apart, except for the difference between the G and the B string, which is a major 3rd.. It’s just the unique way a guitar is tuned. So to play a 4th (across most strings), you just need to fret the same fret across two string.

Diagram showing intervals of a 4th across guitar strings.

Of course, since the G and B strings are only a 3rd apart, you need to add an extra fret there, as shown with the blue dots on the diagram.

How To Practice 4ths On Guitar

Adding 4ths into your playing currently be easier. They occur so naturally on the guitar! The 4th of a scale also appears in both the minor pentatonic scale and the Blues pentatonic scale, so using it in soloing is easy. What’s more, it’s a convenient interval to play if you want to play two notes at once in a solo or riff.

And that’s 4ths. I appreciate this is a relatively short article, but 4ths are pretty easy to find compared to other intervals on guitar.

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