We found in the Uke Camp lesson on the F-Chord Family and its base Key of F, there is a Bb (flat) instead of B. We also see an F#(sharp) in the key of G and its Chord Family. What is a sharp and a flat and what causes it? It has to do with the scale interval.

Scale Intervals

All scales have a set interval of tones that follow a pattern of whole or half steps. In the major keys, the intervals follow the pattern of:
Whole Step | Whole Step | Half Step | Whole Step | Whole Step | Whole Step | Half Step

On your uke fretboard, a whole step is two frets and a half step is one fret.

So, the scale in the key of F the notes are: F G A Bb C D E. To find them on the fretboard, you can begin with the F note (2nd string, 1st fret) then skip a fret to find G, skip a fret to find A, then one fret to find Bb, then two frets to find C (remember the whole-whole-half-whole-whole-whole-half?). Skip a fret to find D, then skip a fret to find E, then step one fret (the very next one) to find F again.

The notes of B and C are always next to each other on the fretboard (they are a half-step apart) the same is true for the E and the F. All the other notes are a full step apart.

So what about that Bb? The A and the B are a whole step apart, but, in the key of F that is where the interval pattern calls for a half step, which means the very next fret. So instead of using the B, we have to move down one fret to the Bb to make it a half step.

In the key of G the interval pattern calls for a whole step at the E and the F (remember the E and the F are always a half step apart?). To maintain the “whole whole half whole whole half” pattern we’ll have to move up two frets to maintain the proper interval. So you will move up two frets from E to F#.

Move up the fretboard one step to make a note sharp, and fall back to make a note flat.

Enharmonic Notes

To add to the confusion, moving up or down one fret can produce two different names even though it is the same note!

For instance, if you move up one fret from a G the note can be named a G# or an Ab - because it is one step up from a G (so it is sharp) and one step down from the A (so it is flat).

These notes are said to be “enharmonic”. Which name you use for that note is determined by which key you are using. It is still the same note and sound.