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63Thinking-ladders: A suggested out for a set of puzzlesPhilosophical Papers 1 (1): 11-26. 1972.No abstract
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49The sceptical chemist and the unwise philosopherRhodes University. 1960.Rhodes University Libraries
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93The role of imagination in judgments of factPhilosophy and Phenomenological Research 29 (1): 34-58. 1968.