9.1 Hammer-ons and Pull-offs video
Tunefox Guitar Lesson #9
Hammer-ons and Pull-offs are examples of left hand articulations on stringed instruments called slurs.
A hammer-on is when you pluck a string with your picking hand and then you fret a different note with your left hand. You're bringing your finger down with enough force to make another note sound. For example, play the 4th string open. Now drop your middle finger of your fretting hand down on the 2nd fret 4th string. You're only plucking once but you're creating the sound for two different notes. The pull-off is essentially the opposite of the hammer-on in that you're starting higher in pitch and 'pulling off' that note to bring you to a lower pitch. You'll pluck a note and then pull that note away from your body to create another note. Watch the lesson below for a demonstration.
Hammer-ons and Pull-offs Guitar video lesson
This tab shows the hammer-on first and then the opposite movement, or the pull-off.