A foundational philosophical treatise that begins with methodical doubt—suspending belief in all uncertain knowledge to discover an indubitable starting point in the thinking self—then develops arguments for the existence and perfection of a benevolent God to secure the reliability of clear and distinct ideas, articulates a sharp distinction between mind (thinking substance) and body (extended substance), and defends the possibility of certain knowledge about the external world; the work is followed by selections of contemporary objections and the author’s replies that probe issues such as divine deception, the nature of sensation and perception, and the relation between thought and extension.