We propose a theory of how systems of thought aiise on the basis of differing cultural practices and argue that the theory accounts for substantial differences in East Asian and Western thouaht processes. We find East Asians to be more holistic, attending to the entire field and assigning causality to it. making relatively little use of categories and formal logic, and relying on ''dialectical'' reasoning. Westerners are more analytic, paying attention primarily to the object and the categories to which it belonas and using rules, includina formal loaic. to understand its behavior. The two tvpes of cognitive processes are embedded in different naive metaphysical systems and tacit epistemologies. We speculate that the origin of these differences is traceable to markedly different social systems. The theory and the evidence presented call into question long held assumptions about basic cognitive processes and even about the appropriateness of the process-content distinction.