When we play a regular scale we can't use just any seven notes. How do we know which ones are the right ones? Since most bluegrass music is played in the key of G (the actual key may vary if we use a capo, but we are still using chords and fingerings played as if we are in open G) we could easily memorize the notes in the G scale. For most people this is all they need. However, like most things in music, there is an underlying pattern to all major scales regardless of key.

To understand this we need to look at the chromatic scale. We know that the chromatic scale has eleven different notes in it. We name the notes using letters from A to G. To create the whole chromatic scale we add sharps and flats to indicate notes between the letter notes. For example if we start with the open third string again when we fret the first fret we are playing a G sharp note. The second fret is A and the one after that is A sharp. You might guess that this pattern continues until you get to the twelfth fret. Unfortunately if it did we would end up with thirteen notes instead of eleven.

The answer is that two pairs of the letter notes don't have a fret between them. These two pairs are B and C, and E and F. You might ask who thought this up but it just seems to have happened some time is the distant past. Here is one way to write the whole chromatic scale:

A A# B C C# D D# E F F# G G#

This scale only uses sharps to designate the notes between the letters. They can also be written using flats instead of sharps. Sharps indicate a letter note that has been raised one fret in pitch and flats are lowered one fret. The way this works out is that sharps of one letter note are also flats of next higher letter note. The other version of the scale looks like this:

A Bb B C DbD Eb E F Gb G Ab

These two scales actually sound the same. For example, G# and Ab are both the note you get by fretting the 3rd string at the 2nd fret. Originally in European music these notes weren't the same. Most instruments only played in one key. I don't know any of the mathematics about this, but the human ear can hear very tiny differences between 2 notes. When instruments are made to play in only one key some of the notes are slightly different from the system we now use. Somewhere in the 17th century or so people began making instruments to play in all keys. The most important to us today is the piano. It required a few comprimises to make this all work and most of the time we don't know the difference. If you've ever had trouble getting the 2nd string in tune on either a banjo or guitar you've heard the problem without knowing it. If you tune the open string to a B note with a tuner, you will find that when you play a D note on the 3rd fret of the 2nd string it's a little flat. B is the 3rd note of the G scale. Notes having this relationship to the first note of any key being played in are a teeny bit off from what your ear would really like to hear.

Let's take a final look at scales. For simplicity we'll use the C major scale which is:

C D E F G A B C

Compare this to the chromatic scale starting on C:

C C# D D# E F F# G G# A A# B C

We see that there are sharp notes between every letter note except for E and F and B and C. This means that there are two frets between all letter notes except E and F and B and C which are adjoining frets. Another way to look at this is that there is no fret between the 4th and 5th and 7th and 8th (octave) notes of the scale. This is the key to understanding all major scales.