George Berkeley (1685–1753) was an Irish philosopher and clergyman. He is known as the founder of idealism—the view that the external world does not exist independently of the human mind. He also believed in immaterialism—the theory that there is no matter in the universe.

So what are objects like trees and objects we think we see according to Berkeley? They are collections of ideas or sensations that exist only if perceived. Thus, all experiences are illusions. Remember the question: If a tree falls in a forest and no one sees it, did it really happen? According to Berkeley, neither the tree nor the forest would exist if not perceived by some mind. Thus, Berkeley is famous for the statement: Esse est percipi – “to be is to be perceived.”

Berkeley had a great effect on higher education while in America. He assisted in the development of Yale and Columbia universities and a number of other schools.