“To exist is to be perceived” is a famous saying of the British philosopher Berkeley.

Berkeley's formula is to be is to be perceived. It obviously means that if something cannot be perceived, then it does not exist. Berkeley himself was well aware of the problem. Because he said: "Don't think that I have abandoned existence (Existence), I just pointed out the meaning of this word as I understand it." Furthermore, saying that something's existence depends on its being perceived does raise the question of whether it exists when it is not perceived. For Berkeley, the key to the whole question lies in the word exist: "The table on which I write I say exists, that is, I see and feel it. If I do not learn, then I say it Existed. Therefore, it means that if I still learn, then I may perceive it, or other spirits can perceive it.” Here, Berkeley means that the word “exists” has no other meaning. , just what is said in the formula is perceived. For there is no case where we use "exists" without assuming that the mind perceives something. To those who contend that material things have some absolute existence independent of perception, Berkeley replied: That seems incredible to me. To be precise, he said: "The horse is still in the stable, and the book is still in the study, even if I am not there. But because I know that nothing can exist without perception, and the book and the horse still exist because there are still Others perceive them."

How did Berkeley arrive at this novel idea? In his New Treatise on Vision, he argued that all knowledge depends on vision and other sensory experiences. In particular, Berkeley argued that we never have a sense of space or magnitude, we only have a sense of things when we look at them from different angles. I also cannot see distance, the distance of objects is indicated by our experience. Everything we see is the quality of things that our visual senses can sense. We cannot see the closeness of objects. We only see differently when we move closer to them or farther away from them. The more Berkeley paid attention to the mechanism of his own mind and wondered how his ideas related to objects outside the mind, the more certain he became that he would never discover any objects independent of his ideas. "When we try our best to think about the existence of external objects, we are always thinking only about our own ideas." "There is nothing simpler than to imagine the trees in the park or the books in the bookcase without seeing them. But all this, except forming in your mind a certain idea of ??a book or a tree. But aren't you thinking about them all the time? ?” He concluded that it was absolutely impossible to think about things without connecting with the heart. We never experience things that exist outside of us and are as separate from us as distance suggests.