Metaphysical solipsists argue that there are indeed no minds but one's own and that attempting to prove the existence of another mind is futile. Proponents of this view argue that the world outside one's own mind cannot be known and indeed might be nonexistent. There are weaker versions of metaphysical solipsism, such as Caspar Hare's egocentric presentism (or perspectival realism), in which other persons are conscious but their experiences are simply not present.