Pentatonic scales are scales formed of five notes (from the Greek pente: five). These scales have been very much used in the folk music of various countries. More recently, composers such as Claude Debussy and Maurice Ravel have used them in their music.
Although any scale formed of five notes may theoretically be called pentatonic, the most common forms are the following:
Those two types of pentatonic scales may be related to major and minor scales. The first one looks like a major scale without degrees IV and VII. The second one looks like a minor scale without degrees II and VI. Both contain the same notes but differ by their tonic. Because of this similarity, some theorists have named them major pentatonic and minor pentatonic.
The Minor Scale
As the major scale, the minor scale has 7 notes. However, it has three variants: the natural minor, the harmonic minor, and the melodic minor. Those variants differ in the manner degrees VI and VII are altered.
In the natural minor scale, all notes appear with the same accidentals as in its relative major. Hence the name of natural:
Minor natural scale
Half-steps are found between degrees II-III and V-VI.
The degree VII of a minor scale is very often raised. The resulting scale is referred to as harmonic minor scale because the raising of degree VII is often harmonically motivated. Raising that note forms the dominant chord or dominant seventh chord on the fifth degree of the scale:
Minor harmonic scale
Beside raising degree VII, degree VI may also be altered. The resulting scale is called melodic minor scale. The main purpose of this accidental is to facilitate the melodic movement from degree VI to degree VII, avoiding the augmented second that is formed in the harmonic minor scale. Therefore, it is referred to as the minor melodic scale:
Minor melodic scale