In the context of the guitar, music theory is referred to as guitar theory encompassing chords (harmony), scales (melody), and timing (rhythm).
Unfortunately, many beginner guitarists shun music theory believing it to be too complicated.
But, learning the basics isn’t difficult and creates a real foundation for learning guitar and communicating with other musicians.
In the following guide, we’ll provide an overview of guitar theory, from the perspective of a left-handed guitarist, including what sound is, notes and intervals, scales, chords, and rhythm, and provide links to our more in-depth resources on each of the topics covered.
*Note: much of the introductory information is not specific to right or left-handers. But our more in-depth articles introduce left-handed chord charts and scale diagrams and descriptions of how to use them.
What is Sound?
Sound is caused by the energy of an object vibrating, which creates waves of pressure known as sound waves. Soundwaves travel by displacing particles in the surrounding medium, e.g. air. and upon entering the eardrum, are amplified and transferred as electrical impulses to the brain where the characteristics of the soundwave and interpreted.
These characteristics include the length of the soundwave (wavelength), the time taken to produce the soundwave (time period), the height of the waveform (amplitude/volume), the number of completed soundwaves passing a given point per second (frequency/pitch), and the distance in meters a sound wave travels per second (speed).
This is what sound essentially is, the brain interpreting changes in pressure caused by an object vibrating.
If a tree does fall in the forest and no one is around to hear it, does it make a sound?
How Sound Becomes Music
The most important of the 5 characteristics concerning guitar theory is frequency, as this defines pitch, allowing us to define notes that can then be used to form the building blocks of music. Frequency is measured in Hertz (Hz) and represents the number of completed soundwaves passing a given point per second.
On the guitar, frequency and pitch are simple to demonstrate.
For example, when plucking an open string the note played sounds lower in pitch than when compared to the same string being fretted.
This occurs because the length of the guitar string able to vibrate has been shortened, reducing its mass and allowing it to vibrate faster, increasing the note’s frequency, and therefore raising its pitch.
The human ear can detect sound between 20 and 20,000Hz (20Khz). However, we hear frequencies that are multiples of the same frequency as the same note.
If that sounds confusing let me explain.
Take the note of middle C, which is 256 Hz (256 soundwaves per second). If that number was doubled (512) or halved (128) the brain would recognize it as the same note, it would sound higher or lower in pitch, but we still recognize it as the same. In simple terms, this means each octave is double the frequency of the one lower than it.
There are 10 octaves between 20 and 20,000Hz.
Musical Notes
The 12 Tone Equal Temperament System
We’ve been over what sound is and how the brain perceives it, how pitch is defined by frequency e.g. the number of completed soundwaves per second. And, we also know that we can hear between 20 and 20,000 Hz and octaves are double the frequency of the octave below it.
The next step in understanding how music works is to divide octaves into notes that we can use to make music.
Octaves are divided into 12 equally spaced sections on a logarithmic scale. You can read more about how that works here if interested, but what’s important to understand is that octaves are divided into 12 notes.
This is known as 12-tone equal temperament (12 TET). The notes simply follow the alphabet and are represented by the chromatic scale:
| A | A# | B | C | C# | D | D# | E | F | F# | G | G# |
The chromatic scale contains all the available notes in our musical system. 7 of these are natural notes and follow the order of the alphabet: A, B, C, D, E, F, G
The remaining 5 notes are accidentals e.g. sharps (#) and flats (b). They are enharmonic, which means they are of the same value musically. This means A# is of the same value as Bb, C# is of the same value as Db, and so on.
Most of the time you will come across sharps (#) being used when ascending in pitch and flats (b) when descending, however, when used in scales both can be used to prevent repeating a note letter within the scale.
Knowing the order of the chromatic scale is key to learning the fretboard.
Keys
A musical key is defined by a specific set of pitches or notes, known as a scale, arranged in a particular order. Each key has a tonic note, which serves as its central and most stable point.
The relationship between the tonic and the other notes in the scale creates a unique tonal center and a distinct mood or atmosphere. Composers and musicians use keys to establish the framework for a piece of music, determining which notes and chords are most prominently featured.
Changing keys within a composition, known as modulation, can evoke different emotions or provide contrast. Musical keys are a fundamental tool for structuring melodies, harmonies, and chord progressions, allowing for the rich diversity of musical expression found across various genres and styles.
Scales
As you can see, in the process of explaining music we’re simply breaking things down into smaller and smaller increments. And while the chromatic scale is technically a scale, it contains all the notes used in music so isn’t as useful in terms of composing music as scales derived from the chromatic scale.
What are scales?
Scales are simply series of notes taken from the chromatic scale and placed in ascending or descending order. The notes from scales can then be used to play in key, both harmonically (in the form of chords) or as single notes.
Key refers to the tonal center e.g. the notes played are derived from a specific scale (defined by the first note (tonic) of the scale and sound good when played over chords within the same key.
In terms of music theory, the most important scale is the major scale. It is foundational to music in terms of harmony and is used as a relative scale for all other scales.
Other useful scales for guitarists include the minor pentatonic scale, blues scale, and natural and harmonic minor scales.
Each note of a scale is known as a scale degree.
Relative Keys
The relative minor is a fundamental concept in music theory that plays a crucial role in understanding the relationships between major and minor scales.
Simply put, the relative minor of a major scale is a minor scale that shares the same key signature (the same number of accidental notes e.g. sharps and/or flats) and consists of the same notes as the major scale but starts on a different note.
Understanding relative minors is essential for musicians as it helps in creating harmonic progressions, composing music, and improvising.
This note, which becomes the tonic or root of the minor scale, is located a minor sixth interval below the tonic of the major scale. For example, in the key of C major, the relative minor is A minor, as both scales share the same key signature (no sharps or flats) and use the same set of notes.
The circle of fifths (pictured above) is a useful tool for determining the relative minor of a major key or vice versa.
To establish the relative minor of a major scale, simply locate the key directly inside the major key on the circle of 5ths, as highlighted above. In this example, Gm is the relative minor of Bb major.
Intervals
Intervals differ from notes as they describe the distance between notes, defining the relationship and how a melody or harmony sounds. While notes are absolute, intervals are relative e.g. the type of interval is defined by the distance between notes, not the notes themselves.
An octave, as outlined above is a type of interval with 12 notes between. The smallest interval is the semitone aka half step which is the interval between a note and the note nearest. e.g. the interval between A and A# is a semitone. A whole tone (aka the whole step) spans two notes or two frets on a guitar string.
Intervals are important in terms of harmony as they define the quality of chords. Quality is not a measure of how good something is in music, it refers to whether the chord is major, minor, diminished, or augmented.
For example, the 3rd scale degree of the major scale is the major third. If a chord contains a major third the chord is major. If alternatively, the chord contains a minor 3rd, the chord’s quality is minor.
Chords
Chords are built from scales.
Chords can be constructed using scale degree formulas based on the major scale. For example, to build a major triad (chord containing three notes) the chord must include the scale degrees 1, 3, and 5 of the corresponding scale. The same chord can also be assembled using intervals e.g. root, major third, and a perfect fifth.
A major chord consists of the root (1st), 3rd, and 5th scale degrees of the major scale. When building minor or other types of chords we still refer to the major scale. For example, the natural minor scale is constructed using the root, flattened third and 5th scale degrees of the major scale. A flattened 3rd is a note one semitone below a major third, aka a minor third.
Usually, chord charts are formatted for right-handers which can be confusing for left-handed guitarists.
Rhythm
All music has rhythm, it provides structure to music.
While rhythm is discussed far less than melody and harmony in terms of guitar theory, developing timing might be one of the most important aspects of playing guitar.
But, timing comes down to practice, in terms of understanding what it is, rhythm is the study of time and space.
There are three key areas to rhythm:
The Beat – This is the pulse of the song, what you would tap your foot to.
Tempo – The speed of the beat. For example, 120 BPM would mean the piece of music contains 120 individual beats per minute.
Subdivision: How the beat is divided. We’re typically talking about note values when discussing sub-division e.g. whole notes, 8th notes, and 16th notes.
Final Thoughts
I hope the information above helps take away some of the mystery surrounding how music works. At the end of the day, all sound is vibration, defined by the characteristics of the soundwave’s form and then broken down into individual notes used to form the foundations of music e.g. melody, and harmony, with rhythm providing structure.
If interested in more in-depth information on each of the fundamental aspects discussed, be sure to click on the links included in this article (all written from a left-handed guitarist’s perspective).
