In philosophy, Ryle's regress is a classic argument against cognitivist theories, and concludes that such theories are essentially meaningless as they do not explain what they purport to. Overview The philosopher Gilbert Ryle was concerned with what he called the intellectualist legend (also known as the "Dogma of the ghost in the machine," the "Two-Lives Legend," the "Two-Worlds Story," or the "Double-Life Legend") which requires intelligent acts to be the product of the conscious application of mental rules. In other words Ryle was attempting to combat Cartesian dualism. A fine summation of the position which Ryle is combating is the famous statement by Ralph Waldo Emerson that, "The ancestor of every action is a thought." In sharp contrast to such assertions, which rule out any other possible parentage to actions by the use of the word "every," Ryle argued in The Concept of Mind (1949) that the intellectualist legend results in an infinite regress of thought: According to the legend, whenever an agent does anything intelligently, his act is preceded and steered by another internal act of considering a regulative proposition appropriate to his practical problem. [...] Must we then say that for the hero's reflections how to act to be intelligent he must first reflect how best to reflect how to act? The endlessness of this implied regress shows that the application of the criterion of appropriateness does not entail the occurrence of a process of considering this criterion.(The Concept of Mind (1949), p. 31.) The crucial objection to the intellectualist legend is this. The consideration of propositions is itself an operation the execution of which can be more or less intelligent, less or more stupid. But if, for any operation to be intelligently executed, a prior theoretical operation had first to be performed and performed intelligently, it would be a logical impossibility for anyone ever to break into the circle.(The Concept of Mind (1949), p. 31.) Variants of Ryle's regress are commonly aimed at cognitivist theories. For instance, in order to explain the behavior of rats, Edward Tolman suggested that the rats were constructing a "cognitive map" that helped them locate reinforcers, and he used intentional terms (e.g., expectancies, purposes, meanings) to describe their behavior. This led to a famous attack on Tolman's work by Edwin R. Guthrie who pointed out that if one was implying that every action must be preceded by a cognitive 'action' (a 'thought'