Our enduring fascination with issues concerning language and thought may derive from our sense that these are uniquely human capacities. Despite years of devoted tutoring, even our closest genealogical relatives have yet to acquire the complex and creative linguistic systems that human infants master within the first few years of life (Petitto & Seidenberg, 1979; Premack, 1971). And although members of other species surely manifest sophisticated conceptual and representational capacities, these appear to be accessible to them only under restricted conditions (Rozin, 1976). Findings like these lend substance to the intuition that humans are uniquely endowed with the capacity to build complex, flexible, and creative linguistic and conceptual systems.

Recent research has documented the remarkable rate at which very young children naturally acquire language and develop rich conceptual systems. Researchers estimate that by the time children reach 2 years of age, they learn an average of six new words each day (Templin, 1957). They also have at their command a rich variety of conceptual relations (e.g., taxonomic, thematic, and associative relations) with which they organize and categorize the objects and events they encounter in their lives.