The perfect fourth
- C1
- F4
A perfect fourth is five semitones, from C to F. Inverted, with the lower note moved up an octave, it becomes the perfect fifth.
Its short name is P4. Counted in letters, it spans four letter names, which is why it is written C to F rather than with another name for the same pitch.
The perfect fourth on drop D guitar
On drop D guitar, the perfect fourth is two frets back, the same fret and one fret up when you cross to the next string, and five frets up along one string.
The shape changes from one pair of strings to another, because the strings of this tuning are not evenly spaced. Instead of one shape to learn, there are three of them.
On the staff
On a treble staff, the two notes are written C and F.
The staff shows the two notes one after the other, then together. C to F spans four letter names, which is what the interval's name counts. What you hear is a distance of five semitones.
On the keyboard
A keyboard makes this distance easy to see, where a fretboard hides it. The upper note is five keys along from the lower one, counting black and white keys alike.
C and F on the whole neck
24 notes are marked across six strings.
This diagram marks both notes of the perfect fourth, C and F, everywhere they fall on drop D guitar. You can find every pair shown above somewhere on it.
A perfect fourth above every note
| From | A perfect fourth up |
|---|---|
| C | F |
| D♭ | G♭ |
| D | G |
| E♭ | A♭ |
| E | A |
| F | B♭ |
| F♯ | B |
| G | C |
| A♭ | D♭ |
| A | D |
| B♭ | E♭ |
| B | E |
C–F, D♭–G♭, D–G, E♭–A♭, E–A, F–B♭, F♯–B, G–C, A♭–D♭, A–D, B♭–E♭, B–E
The shapes above do not change with the key, which is the reason to learn an interval as a shape. Only the note names change, and this table gives them for every starting note.