Skepticism was one of Berkeley's main targets in Three Dialogues; the other was atheism. To combat the first of these evil forces, Berkeley conflated appearances and reality by making ideas into "real things;" to combat the second, he set God up in a crucial central role, controlling and maintaining the whole idealist system.

Though Berkeley thinks that sensible objects are mind-dependent, he does not think that they depend for their existence on his mind or your mind or any human mind. Instead, he thinks that they all depend for their existence on God's mind. God brings thing s into existence by conceiving of them and maintains their existence by continuing to conceive of them. God is the ultimate perceiver. From time-to-time God also allows us to perceive these ideas, in certain fixed patterns which we call "laws of nature." For instance, whenever He allows us to have the sensation "seeing fire," he accompanies it with the sensation "feeling heat." He does the same with the sensations "seeing snow" and "feeling cold," and so on.

Berkeley is certain that God must be the cause of all of our sensations, because he notices that these sensations are involuntary. While he can choose to conjure up an image of a watermelon in his imagination, he cannot just choose to see a watermelon with his eyes. There is something else out there which causes him to either see a watermelon or not see a watermelon, regardless of his own will. While most people would say that what is out there determining his sensation is a mind-independent material object (i.e. a material watermelon), Berkeley knows this cannot be the case because he has already shown that there are no such things as mind-independent material objects (or, at least, that there is no reason to believe there are such things). Instead, he concludes that it is God who is causing his sensation. God, he reasons, must contain all ideas inside of Him and allow us to have access to them now and then, in certain patterns.

Positing God as the ultimate backup perceiver means that real objects do not flicker in and out of existence depending on whether any human being is perceiving them. A tree deep in an uninhabited forest exists just as truly and constantly as a tree in a suburban park. For a real object to exist, it must simply be perceived by God. Many people have misread Berkeley on this issue, and, therefore, attribute to him a much less sophisticated view than the one he really held.

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