This book addresses the importance of space and time, of existence unperceived, of publicity and action, and of natural laws. These are examined in a single argument which extends from Chapter Three to Chapter Seven and in the course of which the essential features of any comprehensible world are either assumed or derived. In Chapter Two, before this argument begins, the book introduces and argues for the methods by which this general argument is developed. In Chapter One, the book attempts to show why it is important to consider the essential features of any comprehensible world. This chapter forms a prolegomenon to the inquiry. The argument in it is of a somewhat more impressionistic nature than the argument later in the inquiry; and so it is probably important to point out that the conclusions reached in the inquiry itself are practically independent of the argument of the first chapter. Those that are totally unconvinced by it may still be persuaded by the general argument which follows.