Pieces may have an open instrumentation either by an explicit choice of the composer, or because they come from a time or tradition where it is not customary to specify instrumentation in written music, and there are little certainties as to which instrument should be used for a piece. When the open instrumentation comes from an explicit choice of the composer, it may be because the composition can either be played by many instruments without it affecting its spirit, or because the choice of instrument may be considered a part of the artistic interest of the piece.