|概要||The present paper introduces some key theories and phenomena about “ concept ” known among cognitive scientists to researchers in Articial Intelligence. First, how natural categories are internally represented in our mind is discussed. It may sound counterintuitive, but many behavioral and modeling studies indicate that categories are represented by collection of unsorted exemplars, but not rules nor prototypes. Second, the hierarchical structure of categories is discussed. Although people generally can use taxonomic relations in inferences and reasoning, there are some evidences that category hierarchy is not stored in our memory, but is computed during inferences and reasoning. Third, two theories about symbol systems, namely amodal symbol systems (ASS) and perceptual symbol|
systems (PSS) are discussed. While a modular and amodal semantic memory is the main vehicle of knowledge in ASS, multi-modal perception, action, and affection in the brain ’s sensory-motor system is the key vehicle in PSS. Although, many theories on categorization and concept in cognitive science are built on the basis of ASS, its limitation and PSS ’s potential advantages are discussed.