Rivers exist. That statement would be regarded as a solid fact by almost every normal person. What is a river, exactly? All rivers on earth are fluid that is flowing, (Not just water; Have you ever seen a river of LAVA?) impelled by the force (law) of gravity. A river isn't a thing, it is a state of being-the action of a physical entity. The water isn't a river, then it is, then it is gone. The water is temporary. The river is permanent, though following ...