 Is there any a priori support for ‘There is nothing’? One might respond with a methodological principle that propels the empty world to the top of the agenda. For instance, many feel that whoever asserts the existence of something has the burden of proof. If an astronomer says there is water at the south pole of the Moon, then it is up to him to provide data in support of the lunar water. If we were not required to have evidence to back our existential claims, then a theorist who fully explained the phenomena with one set of things could gratuitously add an extra entity, say, a pebble outside our light cone. We recoil from such add-ons. To prevent the intrusion of superfluous entities, one might demand that metaphysicians start with the empty world and admit only those entities that have credentials. This is the entry requirement imposed by René Descartes. He clears everything out and then only lets back in what can be proved to exist.