My purpose in this study is to explore various forms of irrationality and to name some true irrationals in order to find the bounds of reason. The irrational-if there is such -sets a priori limits to philosophical investigation, for reason must stop before unreason's province. I begin by defining a primary meaning of rational. Forming, then, by opposition, the genus irrational, I analyze the various species of the irrational traditionally offered as true irrationals. I then judge which irrationals do inhere in in nature or in spirit. PART I THE IRRATIONALITY OF THE WORLD CHAPTER] REASON To understand a primary and consistent meaning of the "e;rational"e; it is necessary to see how the term has been used. In the Theaetetus, Socrates, interested in what it means to have knowledge, sets about finding a rational answer and, by his analysis, illustrates a primary meaning of reason. In answer to Socrates' question. What is knowledge, Theaetetus responds with instances of knowledge: Then I think the things one can learn from Theodorus are knowledge - geometry and all the sciences you mentioned just now; and then there are the crafts of the cobbler and other workmen. Each and all of these are knowledge and nothing else. ' Yet a mere enumeration of particulars does not satisfy Socrates.