There are elements of music theory that apply to all western-based music compositions and instruments. One of these is the “semitone”. The most common definition of the semitone is that it is “the smallest musical interval commonly used in western tonal music”.
Instruments used in western music such as the piano, guitar, trumpet, etc. all reflect this basic unit. Each key on a piano is one semitone higher or lower than the adjacent keys. On the guitar frets are one semitone apart. On the trumpet all fingerings are set up to produce tones that are precise semitones within what is called the “chromatic scale”.
For example, the chromatic scale on the trumpet (the scale of successive semitones) represents all the notes capable of being played on the trumpet. (*Yes I know notes can be “bent” up or down by manipulating the way you blow into the mouthpiece, just as you can “bend” notes on the guitar, but these are features of the way different individuals play, as opposed to features of the instrument itself.)
12 Semitones in an Octave
It turns out that an “octave” consists of 12 semitones. That means that if you play an open G note (on the G string), you will find a G up at fret 12 on the same string. If you play a C at A3, you will find another C (an octave higher) at A15 – 12 frets higher.
This is very basic music theory. What is NOT basic music theory is the way the guitar is tuned. Yes, there are different ways to tune a guitar, just as the ukulele, violin, banjo and other stringed instruments use different tuning patterns. The most common way to tune the guitar is to use what is called “standard tuning”: E-A-D-G-B-E – “Eddie Ate Dynamite Good Bye Eddie”.
The most important feature of the guitar fretboard
This tuning results in what I have called the most important feature of the guitar fretboard. That feature is simply this:
Starting at the low E string, each higher string is tuned 5 semitones above the adjacent lower one. The B string (string 2) is only 4 semitones higher than the G string.
Adjacent Notes are 5 Frets Apart
This tuning pattern has many implications for the guitar player, but perhaps the most basic is that you will automatically know that adjacent notes – such as E5 and A5, or D10 and G10 will always be separated by 5 semitones.
Understanding this important fact will help you enormously to find other notes and patterns on the fretboard. For example, if you know that a major third consists of the root note plus a note that is 4 semitones higher, you will know that if C is at A3, then E is at D2 (since C-E is a major third when you are in the key of C.) To repeat, a major third is four semitones above the root.
In the same vein, you will know why playing so-called “double stops” on the G and B strings is fairly easy: because adjacent fret positions are 4 semitones apart – a major third. And minor thirds (which are just 3 frets apart) are also easier to play. Like Chuck Berry you can go up and down these strings through the entire major scale with just two easy fingerings.
Concentrate your efforts on learning one key thoroughly
Just one more comment. This is also a good example of how it would probably be smart to concentrate on just one key (like C or G, for example), thoroughly get to know the relationships and patterns that apply to that key. Then in time transfer them to other keys. Trying to learn many keys all at the same time invariably results in a jumble of confusing patterns.