During flutter, the airfoil oscillates with a large amplitude, which generates vortices at the wake. In vortex induced vibration (VIV) the oscillations of the airfoil are caused by the shedding of vortices. Both flutter and VIV have airfoil oscillations and vortex shedding. How are they different other than the cause and effect relation? And also how to distinguish which one is the cause and which one is the effect for a case where we don't know beforehand whether it is flutter or VIV?