scales have only 5 notes in them.
Pentatonic scales are the basis of many folk songs across the world, and have been used for many hundreds of years. These days, pentatonic scales still feature heavily in pop music, and are a great springboard to improvise from.
The most common type of pentatonic scale is the one produced if you play only the black keys on a piano keyboard – C#, D#, F#, G# and A#. You can tranpose these notes and produce a pentatonic scale that starts on any note at all. If you start on C, you should play C, D, E, G, A.
Taking out the F and B of the usual C major scale, you’re left with a handful of notes which sound good blended together in many different ways. F and B, making the interval of an augmented 4th or a diminished 5th, are harshly dissonant. When you eliminate these notes from the scale, the notes you’re left with are really easy to improvise with (both melody and harmony), because you won’t accidentally play these harsh discords.
Last year, Bobby McFerrin (of “Don’t worry, Be Happy” fame) demonstrated the magic of the pentatonic scale at the World Science Festival. Watch the video closely – how does the audience know which note to sing next?