George Berkeley, also known as Bishop Berkeley, was an Anglo-Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism". This theory denies the existence of material substance and instead contends that familiar objects like tables and chairs are only ideas in the minds of perceivers, and as a result cannot exist without being perceived. Berkeley is also known for his critique of abstraction, an important premise in his argument for immaterialism.
In 1709, Berkeley published his first major work, An Essay towards a New Theory of Vision, in which he discussed the limitations of human vision and advanced the theory that the proper objects of sight are not material objects, but light and colour. This foreshadowed his chief philosophical work A Treatise Concerning the Principles of Human Knowledge in 1710 which, after its poor reception, he rewrote in dialogue form and published under the title Three Dialogues between Hylas and Philonous in 1713.
In this book, Berkeley's views were represented by Philonous, while Hylas embodies the Irish thinker's opponents, in particular John Locke.
The same principles which at first view lead to skepticism, pursued to a certain point, bring men back to common sense. men
Others indeed may talk, and write, and fight about liberty, and make an outward pretence to it but the free-thinker alone is truly free. alone
That neither our thoughts, nor passions, nor ideas formed by the imagination, exist without the mind, is what every body will allow. imagination