Part 3: Hear and measure relationships · Lesson 025 / 117
A fourth is another useful landmark
Recognise a perfect fourth without mixing it up with a fifth.
A perfect fourth spans five semitones and four letter names. C to F is a perfect fourth: C, D, E, F.
Several neighbouring open strings are tuned a perfect fourth apart: low E to A, A to D, D to G, and B to high E. The G-to-B pair is different: it is a major third. This explains why a cross-string interval shape sometimes needs a one-fret adjustment when it passes across those strings.
Do not try to derive every interval shape today. Use one string to measure C–F, then listen to an open-string fourth. The tuning fact is a warning against moving a pattern blindly, not another map to memorise.
Compare fourth and fifth over the same reference. C–F spans five semitones; C–G spans seven. They are different intervals even when the guitar shapes look similar in different places.
Hear it
Fourth
Audio fileFour-beat count-in · 60 BPM · Warm sampled electric guitar. Listen once before playing along.
A concrete example
B string: C at fret 1, F at fret 6, G at fret 8. C–F is a fourth; C–G is a fifth.
Try it, slowly
- Play C–F and C–G slowly.
- Compare open D–G with open G–B.
- Explain why the two open-string pairs should not be assumed to have the same spacing.
Check one idea
Which neighbouring standard-tuning strings form a major third rather than a perfect fourth?
Show the explanation
G and B, strings 3 and 2. That tuning difference affects cross-string shapes.
A good place to stop
You can distinguish a fourth from a fifth and know where standard tuning breaks its fourths pattern.
Return to the example after a short break. A clear explanation matters more than speed.