Music Theory for Guitar

My original plan was to provide references to other materials on music theory but I decided that I’d put one together that was tailored to my approach.  There’a a lot that I’m leaving out but what’s here should provide enough background to understand the material I present elsewhere. This article is not going to have much application, it’s intended to ensure you have the knowledge to understand the terminology I use in other articles.

The Diatonic Scale

Before we talk about the diatonic scale, we need to touch on the chromatic scale.  Western music subdivides the octave (an interval where the frequency doubles) into twelve equal increments, called “semitones”.  Each semitone has a letter assigned to it and sometimes an accidental: flat (♭) or sharp (♯).  Below is a table with an example of one octave of semitones.

While we have twelve semitones in an octave, using all of them all the time doesn’t harmonize well.  Along the way, composers decided that they could use seven of the twelve semitones. They determined that the scale should have five whole steps (intervals of two semitones) and two half steps (semitones) in each octave, where the two half steps are separated from each other by either two or three whole steps. When you apply that rule to the example above,  you can end up with a pattern like this:

 

This pattern of whole and half steps is what is known as the diatonic scale.  You might also noticed that the pattern above somewhat reflects the pattern of black and white keys on a piano.

Intervals

Minor 2nd (example: “Jaws”)

Major 2nd (example: “Happy Birthday”)

Minor 3rd (example: “Iron Man”)

Major 3rd (example: “Blister in the Sun”)

Perfect 4th (example: “Taps”)

Diminished 5th / Augmented 4th (example: “The Simpsons”)

Perfect 5th (example: “Star Wars Theme”)

 

Minor 6th (example: “The Entertainer” — not a lot of good examples)

 

Major 6th (example: “NBC Theme”)

Minor 7th (example: “Star Trek Theme”)

Major 7th (example: “Take Me On” by A-Ha — not my favorite song but M7 examples are hard to come by)

 

Octave (example: “Sweet Home Alabama”)

Chords

The basis of chords is a triad, either root/major 3rd/5th (major chord) or root/minor 3rd/5th (minor chord).  There are other variations, such as augmented, dominant, etc. but as my math professors used to say, “That is left as an exercise for the reader”.

Keys

The key of a song identifies which combination of notes is used in a diatonic scale.  “G Major” indicates the major scale starting on G.  “E Minor” indicates the minor scale starting with E.  Interestingly (and simply) enough, G Major and E Minor indicate the same notes played in the same sequence.

Modes

Just as major and minor scales are sequences of the same notes with a different starting point, you can start a scale at any point in the sequence: these variations are referred to as “Modes”.  I’ll cover the modes in greater depth in a future article.

References

Info on frequency ratios: https://en.wikipedia.org/wiki/Interval_(music)

Article on guitar music theory: http://www.guitarworld.com/guitar-chalk-sessions-guitar-intervals-explained

Intervals on keyboard.  Good general info: http://www.musictheory.net/lessons/31