Thought before language.

To learn language infants must develop a conceptual base onto which language can be mapped. Recent research in infant cognitive development shows that at least by 9 months of age infants have developed a conceptual system sufficiently rich to allow language to begin. Evidence for this system is shown by categorization of objects above and beyond their perceptual appearance, problem-solving, long-term recall of events, and inductive inferences. During the next year, early concepts gradually become refined. However, at the time when language takes off they are often still less specific than many words in daily use, accounting for the phenomenon of overextension of word meaning.