Fascinating and influential, these works formed the foundation of the empirical movement that led directly to the thought of John Stuart Mill, and the later Linguistic Phenomenalism of A. J. Ayer One of the greatest British philosophers, Bishop Berkeley (1685-1753) was the founder of the influential doctrine of Immaterialism - the belief that there is no reality outside the mind, and that the existence of material objects depends upon their being perceived. The Principles of Human Knowledge eloquently outlines this philosophical concept, and argues forcefully that the world consists purely of finite minds and ideas, and of an infinite spirit, God. A denial of all non-spiritual reality, Berkeley's theory was at first heavily criticized by his contemporaries, who feared its ideas would lead to scepticism and atheism. The Three Dialogues provide a powerful response to these fears.