A cognitive approach accepts the fact that natural categories tend to be fuzzy at their boundaries and inconsistent in the status of their constituent members.
Systems of categories are not objectively "out there" in the world but are rooted in people's experience. Conceptual categories are not identical for every speaker of the language.
Categories form part of a hierarchical structure when applied to such subjects as biological classification: higher level: life-form level, middle level: generic or genus level, and lower level: the species level. These can be distinguished by certain traits that put an item in its distinctive category. But even these can be arbitrary and are subject to revision.
Categories at the middle level are perceptually and conceptually the more salient. The generic level of a category tends to elicit the most responses and richest images and seems to be the psychologically basic level.