Cheat Sheet

Guitar Theory For Dummies

Guitar theory is an area of study that explains how you can play, improvise, and compose popular music on the guitar fretboard — and why certain elements of music go together the way they do. Dive into guitar theory by exploring a fretboard diagram showing notes along the 6th and 5th strings; some major scale patterns; Roman numerals and the major/minor chord sequence; and mode names.

Getting to Know the Notes on a Guitar Fretboard

Guitar players must know the notes on the fretboard to keep track of the specific scale patterns and chords they play all over the neck. But rather than memorize every single note in every fret on every string, guitarists do better to just know the natural notes along the 6th and 5th strings. After all, most scale patterns and chord shapes are rooted on these strings. Octave shapes can be used to track other notes in other positions.

The following fretboard diagram shows you the notes along the 6th and 5th strings.

[Credit: Illustration courtesy of Desi Serna]
Credit: Illustration courtesy of Desi Serna

Sample Major Scale Patterns in Guitar Theory

As you explore guitar theory, you'll learn that the major scale is a series of notes played in an ascending and descending fashion. Guitarists use the major scale to play melodies, riffs, solos, and bass lines. Additionally, it's used to play intervals, build chords, and chart progressions.

The following sample patterns show you how to play the G major scale in four positions on the fretboard:

[Credit: Illustration courtesy of Desi Serna]
Credit: Illustration courtesy of Desi Serna

Guitar Theory: Roman Numerals and the Major Scale Chord Sequence

Guitar theory reveals that the major scale is stacked in thirds to make triads and chords. Each scale degree of the major scale produces a triad and major or minor chord. Starting with the first degree of the major scale, the chord qualities go as follows:

major-minor-minor-major-major-minor-minorb5 (also called a diminished triad)

This seven-chord sequence is one of the most important patterns in music. When it comes to playing chord progressions, musicians refer to this pattern by using uppercase Roman numerals to represent major chords and lowercase Roman numerals to represent minor chords.

The following chart will help you keep track of the system:

Uppercase Roman numerals: I-II-III-IV-V-VI-VII
Lowercase Roman numerals: i-ii-iii-iv-v-vi-vii

Here's what this naming system looks like in action when you apply it to the major scale chord sequence and the key of G, specifically:

Major Scale
I-ii-iii-IV-V-vi-viib5
G Major Scale
G-Am-Bm-C-D-Em-F#mb5
[Credit: Illustration courtesy of Desi Serna]
Credit: Illustration courtesy of Desi Serna

Guitar Theory: Modes of the Major Scale

As you study guitar theory, you'll hear terms like mode, tonic, and scale. The most common scale in music is the major scale. It includes seven degrees, or pitches, and involves seven steps or intervals. When you play the major scale beginning on its 1st degree, you create the familiar "Do, Re, Mi . . ." sound. But the starting position of the major scale isn't always the 1st degree.

What is a mode?

Music often centers on other degrees in the major scale besides the 1st one. For example, start a major scale on the 6th degree and you create what is known as the minor scale (also known as the relative minor or natural minor). The 1st and 6th degrees of the major scale produce the major and minor scale. In music, you say that the scale has these two different modes.

The major scale has more modes than just the 1st and 6th degrees. The truth is, any scale degree can be used as the starting point. However, the major and minor modes are the most commonly used scales in music. In fact, they're so common that they're not usually thought of as modes. Instead, they're thought of as plain or natural scales. It's only when music centers on one of the other degrees in the major scale that the music is considered modal.

Of modes and tonics in the major scale

There are seven degrees in the major scale, and each one can function as the tonal center, or first tone (tonic) of the scale. Long ago, the Greeks named each one of these modes. The names are as follows:

  • I. Ionian: More commonly known as the plain major scale.

  • ii. Dorian: A type of minor scale with a major 6th. Fairly common. "Oye Como Va" by Santana is an example of a song that centers on the 2nd degree of the G major scale using the chord progression Am7-D9. You say that it's in A Dorian mode.

  • iii. Phrygian: A type of minor scale with a flattened 2nd. It has a Spanish flavor to it, but it's not used much. One example is "The Sails Of Charon" by Scorpions, which centers on the 3rd degree of the G major scale, producing B Phrygian mode.

  • IV. Lydian: A type of major scale with a sharpened 4th. Occasionally used temporarily in a song before the music settles on a more stable tonic, such as I. Listen to "Man on the Moon" by R.E.M for an example of C Lydian, the 4th mode in the G major scale.

  • V. Mixolydian: A type of major scale with a flattened 7th. Very common, almost as much so as the plain major scale. You should recognize this mode anytime you start on a major chord and then move down a whole step to another major chord. A change like that is almost always V-IV. "Seven Bridges Road" by the Eagles centers on the 5th degree of the G major scale, producing D Mixolydian mode.

  • vi. Aeolian: More commonly known as the natural or relative minor scale.

  • vii. Locrian: Not used. The 7th triad has a flattened (or diminished) 5th making the chord too unstable to function as a usable tonic.

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