 Not all changes seem to be merely the (loco)motions of bodies in physical space. Yet since antiquity, in the western tradition, this kind of motion has been absolutely central to the understanding of change. And since motion is a crucial concept in physical theories, one is forced to address the question of what exactly it is. The question might seem trivial, for surely what is usually meant by saying that something is moving is that it is moving relative to something, often tacitly understood between speakers. For instance: the car is moving at 60mph (relative to the road and things along it), the plane is flying (relative) to London, the rocket is lifting off (the ground), or the passenger is moving (to the front of the speeding train). Typically the relative reference body is either the surroundings of the speakers, or the Earth, but this is not always the case. For instance, it seems to make sense to ask whether the Earth rotates about its axis West-East diurnally or whether it is instead the heavens that rotate East-West; but if all motions are to be reckoned relative to the Earth, then its rotation seems impossible.