Book introduction

　This book aims to clarify the meaning, historical significance, and scope of “theories of ideas”, the series of accounts on “ideas” by Baruch de Spinoza, a seventeenth-century Dutch philosopher. First, Spinoza’s theory of ideas was influenced by René Descartes to a degree such that it is almost impossible to understand without it. For this reason, I begin by exploring and attempting to grasp the Cartesian theory of ideas, and then seek to elucidate the uniqueness of Spinoza’s. As shown in the subsequent chapters, Spinoza’s account emphasizes the existence or reality of ideas themselves. At this point, I argue that Spinoza’s theory of ideas is as unique as the philosophical system that underpins this theory, compared with his contemporaries, including Descartes.