The period between 1945 and 1952 marked the development of Professor Ryle's conception of the principles of inference as performance rules. This development has paralleled that of his now well-known distinction between knowing-how and knowing-that. Indeed, the former is a corollary to the latter. Beginning with the inaugural address to the Aristotelian Society in 1945 (2) and reaching full fruition in The Concept of Mind in 1949 (4), it finds its most detailed and illuminating expression in “‘If’, ‘So’, and ‘Because’,” which appeared in 1950 (5). The present essay will attempt to explore this conception of rules in some detail, in the hope of clarifying the nature of Professor Ryle's views on classical logic and on certain problems within the philosophy of logic. Professor Ryle belongs, if his views may be so labeled, to the school of informal language analysts. On the other hand, we incline more toward formalism. We tend to agree with those philosophers who consider certain schemata indispensable tools for the solution of philosophical problems. Logic and the philosophy of logic are, as everyone knows, the areas in which the formalists’ technique originated. In these areas it is accepted by virtually everybody. The only recent exception is a group of English writers, many of whom take their inspiration from Ryle. One may hope, then, that the present criticism of Ryle's view from the other standpoint will throw some light on both positions. What follows falls naturally into two parts. The first deals mainly with Ryle's objections to current logical theory, the second with his own philosophy of logic.