  Even if we grant that we cannot tell whether it is our train that is  gliding along with a constant velocity or the train that we see  through the window, we might nonetheless maintain that we can tell  – by, say, the sudden jerk we feel – if our train has  just accelerated by increasing its speed, or – because we feel  ourselves pushed against the wall – that it is rounding a sharp corner. Leibniz, however, seems to deny   this,[27]  insisting instead that “no eye, wherever in matter it might be  placed, has a sure criterion for telling from the phenomena where  there is motion, how much motion there is and of what sort it is,  or even whether God moves everything around it, or whether he  moves that very eye itself” (AG   91).[28] 