As of right now, the only scales we have covered are those with 7 different pitch classes with a repeat of a note at the octave.
But there are other common scales that use less notes.
The pentatonic scale (the “penta” prefix meaning “five”) is a scale built from 5 different pitches within its pitch class collection with a repeat at the octave. This scale is commonly used in many genres of music from rock, to jazz, folk, pop, world, etc.
A good argument as to why these scales are so widely used is because they avoid certain dissonances. You will see why shortly.
First, let’s start by building the major pentatonic scale.
A major pentatonic scale is made up of a pattern of notes set apart from each other in an ascending manner of M2-M2-m3-M2-m3 from the root to the octave:
Notice how the scale and intervallic distances do not contain anything to form dissonances (m2, A4, d5, M7, etc.). Also, take a look at how the scale is very similar to that of a regular major scale, but is missing the fourth and seventh scale degrees.
Just like every major scale has a relative natural minor scale, so will every major pentatonic scale have a relative minor pentatonic scale.
To build a minor pentatonic scale, you just have to use the same pitch class collections as the relative major pentatonic scale, but start on the sixth scale degree. Or, you can also build it by using the intervallic pattern of m3-M2-M2-m3-M2:
Similarly, it looks like a natural minor scale, but it is missing a few members. Hence, that is why the pentatonic scale is called “penta;” because it is 2 pitches short of a major or natural minor scale, making it 5 instead of 7.
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Daily Music Writing Tips - Blog by Bryan M. Waring 