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 ''rational'' 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.