George Berkeley was born in 1685 near Desert Castle, Ireland. He graduated from Trinity College, Dublin, where he was introduced to philosophies of Descartes and Locke. Berkeley's subjective idealism means all things are constituted by mind and its ideas and things (ideas) depend on perception for their existence. His theory is focused on the citation "to be is to be perceived." Berkeley thinks that in the absence of a perceiver, the tree's sound, color, taste including its sound waves, color frequencies, shape, motion, coconuts, the sand, mountains and the entire island cease to exist. Berkeley's philosophy can be stated as "Ideas exist only in minds, All things are Ideas.

Therefore, all things exist only in minds." Everything in this philosophy is based on "idea." The mental representation of something in the external world, say a table, such as brown, rectangular, smooth, flat and four legged. If so, Berkeley's first premise, "Ideas exist only in minds" can't be objected. Berkeley rejects his predecessors' view that ideas represent material objects in the external world, he says those realities are "ideas." Berkeley conceived his theory of reality as four parts. First part of plan including, second, psychology and ethics, third, physics, and fourth, mathematics.

Berkeley's three most important works are Essay Towards a New Theory of Vision, Treatise Concerning the Principles of Human Knowledge, and Three Dialogues between Hy las and Phillonous. Berkeley defended his thesis with the following considerations. 1) The impossibility of having ideas that is similar to realities, which are essentially different from ideas. Mind and Matter are not separated and there is no difference between our ideas and reality.

2) The impossibility of framing any meaningful idea of different from ideas. Matter is a meaningless world, it is devoid of any qualities, and it is only by means of the qualities of something that we can have an idea of it, and we cannot know or talk about something we have no idea of. 3) The impossibility of thinking of something that is un experienced. You cannot think of something without thinking of its qualities, and to think of qualities it to perceive or experience them. 4) The impossibility of separating primary qualities from secondary qualities, which makes primary as well as secondary qualities subjective. Secondary qualities are accepted as subjective and requiring a perceiver, and since primary qualities must go the same way as secondary qualities, primary qualities too must be subjective.

5) The impossibility of absolutizing even primary qualities, which thus turn out to be as relative as secondary qualities. We have the natural tendency to think that though colors, sounds, and tastes disappear with the perceiver, qualities like shape, size, and motion continue even when unperceived. But take a shape, for example rectangle. Is there really anything such as a perception of rectangle? Do two people perceive the same shape? Infact there is infinite number of viewpoints or perspectives.

All qualities are ideas in the mind of perceiver. Berkeley introduced God as infinite mind, who perceives all things at all times. This preserves both the reality of the world external to us but internal to God. Berkeley's insistence on subjective idealism has raised many objections. He denied the reality of things, his concern is for the nature of things, specifically, the mental nature of things.