This particular statement is said by George Berkeley. He said it in Latin language - “Esse est percipi” which means to be is to be perceived. According to him we cannot know if an object is, but we can only know if an object is perceived by a mind. Therefore, we cannot think or talk about an object’s being. We can only think or talk about an object’s being perceived by someone. All that we know about an object is our perception of it. The existence of an idea cannot be separated from its being perceived. If an idea or object is not perceived, then it does not exist. Everything in the universe depends on perception.
Though we hold indeed the objects of sense to be nothing else but ideas which cannot exist unperceived; yet we may not hence conclude that they have no existence except only while they are perceived by us, since there may be some other spirit that perceives them though we do not. According to
trees, books and mountains are groups of ideas or sensible qualities and are
therefore as much within the mind as the latter are. A tree is a group of ideas
touched, seen and smelled; a cherry, a group of ideas touched, seen, smelled
and tasted. The sensible qualities or ideas without which we should have no
conception of a tree or cherry, don’t belong to some unseen, untouched,
untasted substance, for the very conception of such a “something I know not
what” is incoherent and rests upon the false view that we can conceive
something in complete abstraction from ideas of sense. Berkeley
According to Berkeley we perceive trees and cherries directly by seeing, touching and tasting them, just as the plain man thinks, we do, whereas his opponents regard them as perpetually hidden from us by a screen of intermediaries that may be always deceiving us.
considered that by this view he had
refuted skepticism of the senses, for, according to his theory, the objects of
the senses are the things in the world: the trees, houses and mountains, as
compounded of sensible qualities or ideas cannot exist without the mind. Berkeley
Gilson, Etienne and Thomas Langan. Modern Philosophy: Descartes to Kant.
: Random House, 1963. New
Berchert M. Donald. “George Berkeley”. The Encyclopedia of Philosophy.
Macmillan Reference. New York