It is a common assumption that basic level categories are cognitive units that share perceptual and linguistic characteristics at the same time. They are taken to be perceptual and functional gestalts designated by words that have a special status with regard to lexical development in children and frequency of occurrence and usefulness in everyday communication. Despite this connectedness of the two aspects of the basic level they do not go hand in hand. The perceptual side of basic level categorization is primary to language and exists independently of it. Basic level categories emerge naturally in the human perceptual-cognitive system as a result of our biological make-up in order to facilitate a proper functioning and orientation in our environment. The linguistic side relies on perception but is at the same time determined by several other factors. Basic level designations do not directly represent perceptual information because they contain additional conceptual knowledge reflecting cultural conceptualizations. This dissociation between the two sides can be seen on the one hand in the inconsistencies between perceptual qualities of entities and the way in which these entities are grouped together in linguistic basic level categories. On the other hand it is revealed through crosslinguistic discrepancies in category boundaries as delineated by words that are considered basic level terms and seemingly correspond in their semantics. An explanation of these phenomena requires that the study does not handle the basic level as one phenomenon in which the perceptual and linguistic aspects merge but keeps the two sides of the basic level apart while paying attention to their specific connections and influences on each other.