George Berkeley (1685-1753) was an Irish philosopher whose primary philosophical achievement is the advancement of a theory he called 'immaterialism' (later referred to as 'subjective idealism' by others). This theory contends that individuals can only directly know sensations and ideas of objects, not abstractions such as 'matter'. Berkeley's work focuses on the idea that existence is fundamentally dependent on perception; famously encapsulated in his dictum, 'esse est percipi' ('to be is to be perceived'). Berkeley is also known for his critique of abstraction and his contribution to the philosophy of mathematics. A staunch advocate of empiricism and a key figure in the formative phase of the British Empirical movement, Berkeley influenced many enlightenment philosophers, including David Hume and Immanuel Kant. His seminal work, 'A Treatise Concerning the Principles of Human Knowledge' (1710), lays out his position that the material world exists only in the experiences minds have of it. Throughout his text, Berkeley dismantles the foundations of materialism and reframes the human understanding of physical reality. His writings not only question the nature of reality and perception but also address the relationship between science and religion, lending to a holistic approach to epistemology and metaphysics. Berkeley's literary style is characterized by rigorous argumentation, yet it remains accessible and has been praised for its clarity and elegance.