Berkeley claims that "to be is to be perceived." If something is said to exist, yet it cannot be experienced in any way, then Berkeley says that the correct metaphysical approach is to deny that it exists at all. Berkeley then goes on to use this approach to deny the existence of material substance (the physical world)! Either defend Berkeley's claim that "to be is to be perceived," OR, offer a counter-example (that is, give an example of something that you believe exists yet cannot be experienced in any way).