Now things are said not to be in several ways; and there can be motion neither of that which is not in respect of the affirmation or negation of a predicate, nor of that which is not in the sense that it only potentially is, that is to say the opposite of that which actually is in an unqualified sense; for although that which is not white or not good may nevertheless be in motion accidentally (for example that which is not white might be a man), yet that which is without qualification not a 'this' cannot in any sense be in motion: therefore it is impossible for that which is not to be in motion.