A scale is a series of notes played one at a time in an ascending or descending fashion. Guitarists use scales to play melodies, riffs, lead guitar solos, and bass lines. Different types of scales make different patterns on the fretboard that you have to learn and practice.
In popular music, the two most commonly used types of scales are the pentatonic scale and the major scale. From the major scale come modes. The harmonic minor is one more type of scale that’s useful for guitar players to know.
Pentatonic scale
Pentatonic scales are derived from major scales. As the name implies, the pentatonic is a five-tone scale. Because the pentatonic has fewer tones than do major scales (which have seven), its patterns are easier to finger and play on the fretboard. The simple box-shape patterns that the pentatonic scale makes on the fretboard are ideal for getting started with riffing and jamming.
Plus, many of the most recognizable guitar riffs of all time are based in pentatonic patterns. Popular pentatonic songs include “My Girl” by The Temptations and “Purple Haze” by Jimi Hendrix. For these reasons, guitar players often learn pentatonic scale patterns first.
Major scale
Guitarists use major scales to riff and jam, too. The more melodic a line is, the more likely it is to use a seven-tone major scale. Think “Joy to the World,” which is simply a descending major scale. You hear something similar in the opening to “Friend of the Devil” by Grateful Dead and the chorus to “Wild World” by Cat Stevens.
In addition to using the major scale to play melody, guitarists use it to measure intervals, build triads and chords, add chord tones and extensions, chart chord progressions, and determine keys. You could say that everything is drawn from the major scale or relates to it in some way. Major scale patterns also make minor scales and all the modes.
Modes
Perhaps no other musical topic generates more intrigue and confusion than modes. But the concept is so simple that most musicians miss it. Modes are all the different types of scales that the major scale makes when you change the starting point and pitch center in the scale. This includes the minor scale and all the modal scales that have Greek names such as Dorian, Phrygian, Lydian, and so on.
Far from being an advanced or exotic concept, most music is in some type of mode, and properly identifying a song’s mode is critical to understanding its composition and construction. You don’t learn new scale patterns to play modes. The modal concept is all based on key centers and how major scale patterns are applied.
Harmonic minor scale
The harmonic minor scale is an altered minor scale that plays a very important role in music. Its primary purpose is to create a dominant 7th chord that pulls to a minor tonic, a very strong harmonic resolution.