ABSTRACT
By the time a normally developing child reaches the age of 12, his/her vocabulary may exceed 50,000 words. More importantly, as a relatively competent speaker and listener, the typical 12-year-old will be able to understand almost all of what is said to him/her and to describe most experiences using a complex syntactical system that maps causal and logical relationships, marks the relative importance of various ideas, and combines words to multiply the number of meanings that can be expressed using vocabulary alone. The 12-year-old also will be able to communicate according to an elaborate set of pragmatic rules on the basis of his/her metalinguistic skills. In using productive verbal skills, he/she will access rule-based knowledge related to phonological production, morphology, syntax, semantics, and pragmatics simultaneously and make a myriad of small adjustments based on the conditional rules that modify each of these systems separately and in relationship to one another. To communicate fluently requires auditory and perceptual processing, phonological production, semantic and episodic memory, and the capacity to respond to multiple, transitory, complex social and linguistic stimuli within milliseconds.
