If you're serious about playing the guitar well then unfortunately you'll need to learn some guitar music theory so that you can improvise solos all over the neck, transcribe tunes, learn new music quickly and write your own great songs. However, it doesn't need to be painful or boring if you follow a few simple principles. In this guide, I'll cover the key elements of guitar music theory that you'll need to cover and suggest some strategies for learning them.
The most important thing to remember about learning guitar music theory is that you don't need your guitar to do it! Get some blank fretboard diagrams or draw your own, or invest in a software application so that you can practice drawing out intervals, scales, arpeggios and chords wherever you are ready to transfer the knowledge to your guitar later.
Guitar Notes
The first thing to learn is the notes on the guitar fretboard. You could just go about memorising each string one-by-one, but I think it is better to build your fretboard knowledge organically using root shapes and counting to navigate from a few known points.
Root shapes are the shapes used to navigate between notes with the same name. There are five of these, based on the root notes that appear in the standard open chord forms C, A, G, E and D. Learn these root shapes.
You also need to learn how notes are named - using the letters A-G for the natural notes and a sharp symbol (#) to raise a note by a half-tone (one fret), or a flat symbol (b) to lower it a half-tone. There are normally two frets between each natural note, except B and C, and E and F, which only have one.
Using that knowledge should enable you to start to find notes by navigating from the open strings or twelfth string using counting and root shapes. Work on increasing the number of anchors you have to start from, for example by learning all of the notes on the E strings or all of the notes at the seventh fret.
Intervals
Intervals are vitally important in guitar music theory. These are the distances between two notes and are the basis of the definitions of scales, arpeggios and chords. It is important to learn all of the names of the intervals and also to learn how to play the intervals on the guitar. Each interval will have a number of different ways of playing it depending on how many strings you cross. These are the names of the simple intervals - each one is one fret further away from the root note:
Root, Minor Second, Major Second, Minor Third, Major Third, Perfect Fourth, Tritone, Perfect Fifth, Minor Sixth, Major Sixth, Minor Seventh and Major Seventh.
For each interval you should learn the patterns so that you can start on any root note and find that interval, ideally within a few frets of the start note. There will usually be a couple of options.
Once you are familiar with simple intervals, you can move onto compound intervals - ninth, eleventh etc.
Guitar Scales
Once you've learned intervals then the study of scales becomes more straightforward. Rather than trying to memorise scale patterns physically, memorise the interval formula for a scale and then use the interval patterns that you've learned to build scale patterns. For example, the interval formula for a natural minor scale is:
1, 2, b3, 4, 5, b6, b7
And the interval formula for a major pentatonic scale is:
1, 2, 3, 5, 6
Similarly, you can work on learning the interval formulas for scales from the basic major and minor through the modes and to more exotic scales such as whole tone and diminished. Use the interval patterns you learned to practice writing out scale patterns before transferring them to the guitar.
Arpeggios
Arpeggios are like chords, except the notes are played separately. This makes it easier to learn the arpeggios first as you have fewer concerns about playability since you can play more than one note on a string. Start with learning basic triad arpeggios such as:
Major: 1, 3, 5
Minor: 1, b3, 5
And move on to sevenths and then others such as sixths, sus4 and extended arpeggios such as 9ths and 11ths. There are many to learn - just take a few at a time and practice writing them out before attempting to play them!
Guitar Chords
Finally, we come to guitar chords. These add more complexity than arpeggios as you have to be able to play all of the notes at once, so the physical constraints of the guitar come into play. However, again start with the arpeggios and make choices over which of the notes to pick for a voicing depending on which is most playable and which sounds best in the context that you're using it.
Don't be tempted to reach for the chord dictionary! Learn the chord interval formulas and work out chord voicings to fit your song using the interval patterns that you've learned. It will soon become second nature and you'll be glad that you've taken the time to learn to construct chords yourself when you're confronted with a chord symbol you haven't learned the pattern for, or you want unusual voicings to fit a particular song.
That's been a very brief overview of guitar music theory. It's a wide ranging subject, but I hope that I've demonstrated that it's not an impossible one to master if you take the correct approach.