  Unger's original solution was to reject 1. The concept of a cloud involved, he thought, inconsistent presuppositions. Since those presuppositions were not satisfied, there are no clouds. This is a rather radical move, since it applies not just to clouds, but to any kind of sortal for which a similar problem can be generated. And, Unger pointed out, this includes most sortals. As Lewis puts it, “Think of a rusty nail, and the gradual transition from steel … to rust merely resting on the nail. Or think of a cathode, and its departing electrons. Or think of anything that undergoes evaporation or erosion or abrasion. Or think of yourself, or any organism, with parts that gradually come loose in metabolism or excretion or perspiration or shedding of dead skin.” (Lewis 1993: 165)