The guitar can produce many sounds other than simple fretted notes or chords. One such sound is the harmonic.
Harmonics are basically the ‘overtones’ of a note. They occur naturally every time we pluck a guitar string. However we do not hear them as such since they are very quiet compared to the fundamental note being played.
In some places on the guitar neck we can stop a string dead with our fretting hand, play the string and still hear a note being played. This is a natural harmonic.
The most audible harmonics occur at the 12th, 7th and 5th frets.
To sound a harmonic at the 12th fret of the low E string, say, place the first finger of your left hand so that it is touching the string directly over the 12th fret, and pluck the string. A natural harmonic should sound. Note we are not fretting any strings here, only lightly touching the string to deaden the sound of the fundamental note.
The diagram below shows where the main harmonics lie on the fret board, and what notes are produced:
These harmonics can be used to great effect, especially when playing them in the midst of a standard ‘fretted’ piece of music.
On the guitar, we can also produce harmonics from fretted notes. These are called artificial harmonics. They are played using a harmonic which is 12 frets away from the fretted note. For example, if we are fretting a string at the third fret of the 2nd string, we would therefore need to produce a harmonic on the 15th fret of the 2nd string, since this is 12 frets away from the fretted note (15-3 = 12).
In order to do this, however, since the left hand is occupied fretting the notes, the right hand (picking hand) must lightly touch the string at the desired fret (as for natural harmonics) andpluckthe string at the same time. This is achieved by placing an extended first finger on the string at the correct fret, and while this finger is touching the string follow through in an upward motion to strike the string with the third finger of the right hand.
Once this technique is mastered, the guitarist can produce entire melody lines using harmonics.