Finger substitution is a playing technique used on many different instruments, ranging from stringed instruments such as the violin and cello to keyboard instruments such as the piano and pipe organ. It involves replacing one finger which is depressing a string or key with another finger to facilitate the performance of a passage or create a desired tone or sound. The simplest type of finger substitution is when a finger replaces another finger during a rest; the more difficult type is to replace one finger with another while a note is being played.