Evolving from what used to be solely an upright instrument, the bass guitar has become a staple of modern music. In addition to holding down some rhythm, bass guitars drive the low end playing the root note of the music'c chord structure. The most common electric bass guitars are 4 string basses and 5 string bass guitars that extend the lower range of the bass with a low-B string. 6 string and 7 string basses typically extend the higher range of the bass guitar.