The second of the "British Empiricists" that will be covered is George Berkeley. George Berkeley's A Treatise Concerning the Principles of Human Knowledge argues against the existence of matter, asserting that all things exist only in the mind of God. He refutes the concept of abstract ideas, showing how they are based on language rather than genuine mental constructs. Berkeley contends that sensations are not copies of external objects but are directly perceived and, therefore, reality is fundamentally perceptual.