Sellars defends these claims in his classic article, EPM.  The “Rylean myth” narrated in parts 12–16 of EPM is a thought experiment aimed to convince us that the Cartesian story is not the only possible story about our knowledge of the mental.  The thought experiment hypothesizes a community of proto-humans who lack concepts of inner psychological states, although they possess a complex language for describing and explaining objects and events in the world.  Sellars calls them ‘Ryleans’ in honor of Gilbert Ryle, the Oxford philosopher whose book, The Concept of Mind, argues eloquently for a version of logical behaviorism.  This community possesses a behaviorist’s ability to explain human behavior as well as metalinguistic abilities to describe and prescribe linguistic behavior.  Thus, the community has semantic concepts at its disposal. Sellars claims that such a community can reasonably increase its explanatory resources by postulating unobservable states internal to each person that modulate that person’s responses to the world. Moreover, there is motive to postulate two different kinds of internal states: one kind—thoughts—has properties modeled on the semantic properties of overt linguistic events, while the other—sense impressions—has properties modeled on the properties of perceptible objects.  Thoughts are postulated to explain how the members of the community can engage in complex patterns of reasonable behavior even when silent.  Sense impressions are postulated to explain why members of the community acquire conceptual representations of objects as before them, even, at times, when such objects are not present.  If Sellars’s story is coherent, then the traditional view that our concepts and knowledge of the mental are simply given is not compulsory, and a naturalistic treatment of the mental is potentially viable.