In this exceptional work Berkeley makes the striking claim that physical things consist of nothing but ideas and therefore do not exist outside the mind. This claim establishes him as the founder of the idealist tradition in philosophy. The text printed in this volume is the 1734 edition ofthe Principles, which represents Berkeley's mature thought. Also included are four important letters between George Berkeley and Samuel Johnson, written between 1729 and 1730, an analysis of the Principles, and a glossary.