The Principle of Motion

"If all movable natures are either moved by nature or contrary to nature and by violence, then everything which is moved is moved by something," he says. "It is not through that which itself moves but through something else which moves the mover or it is through itself." He continues: 'Everything which moves moves something and through something for that which moves either moves through itself or through another' And so on until we arrive at a thing of this kind in addition to those who consider the following particulars also will be found to happen,' concludes Aristotle.