 1) Aristotle begins his Book VIII of the Physics raising the question whether motion has come into being and will cease to be, or is eternal “belonging to all beings as their immortal and never failing property” (250b13–14). In order to answer it, he develops various arguments the main one being based on the definition of motion as the actualization of the movable in so far as movable (251a10). If there was a first motion, and since any movable requires a mover, there must have pre-existed a mover and a movable, something capable of setting fire and something capable of burning, for instance. If these have come into being, there must have been a change before the supposed first change that brought them into existence. If they pre-existed without change occurring, a previous change must have occurred that set them into the condition of moving and being moved. By reductio ad absurdum, it is proved that motion has always existed.