George Berkeley was born and educated in Ireland. In his early 20's Berkeley worked out his philosophical theories and also wrote his two most important works, A Treatise Concerning the Principles of Human Knowledge and Three Dialogues Between Hylas and Philonous.
Berkeley was not so precise as was Locke. He dismissed Locke's concept of general ideas, as well as Locke's distinction between primary and secondary qualities. For Berkeley everything boils down to "perception." Behind "ideas" there is no material substance. The entire material world is only a representation or a perception. The only thing, which exists, is the spiritual Self and Berkeley claims that we can have an intuitive certainty of this. All ideas proceed from god. It is God who puts these ideas into our spirit. With Berkeley, once again God is the foundation for all that exists.
Berkeley concluded that we know as real only what we experience and that we experience only our ideas. Therefore for something to be real means that it is the object of some experience. The being of things consists of their being perceived. Berkley's phrase was esse est percipi or to be is to be perceived. It is only in the perception of an object that the object actually exists.
Immediately this conclusion raises the question as to the non-existence of something in the event that it is not perceived by someone. Berkeley's response to this question centered on God's nature. For Berkeley, God is the divine perceiver. God perceives all. Since God perceives my house when no one else does so, therefore my house continues to exist. Again, Berkeley completely rejects the concept of material substance. According to Berkeley, when we say that a thing exists we mean nothing more than that we perceive it.
