Watch the Harmonics online guitar lesson by Pierre Bensusan from DADGAD Explorer: Guitar Intuite

The sound of a string vibrating over its entire length is the deepest tone it can produce, called the "fundamental." According to the physics of a vibrating string, the fundamental creates other higher notes, known as overtones or harmonics. The vibrating string is grazed by the finger, dividing itself over its entire length from two to eight regular intervals. This principle can be applied to all the strings.