Pointing to an object and saying a word is an ambiguous form of reference, because there are an indefinite number of logically possible hypotheses about the meaning of a word. But children are very proficient at learning words. That led us to postulate constraints on the hypotheses that children consider about the meanings of words. In fact, the previous studies have shown that children aged two or over are highly biased word learners (Landau et al., 1988; Merriman & Schuster, 1991). Much of the debate has centered on whether this idea of constraints implies innate and fixed word learning principles, and whether these principles are by nature domain-specific. This paper reviewed the studies concerned with this debate. The previous studies showed that those learning principles emerged in the course of early word learning (Jones et al., 1992), and that children's use of them became more domain-specific with age (Smith et al, 1994). These findings suggest that the principles and the domain-specific use of them may be the consequence of word learning, not innate. But following two facts are notable. First, young children rapidly find the principles in the course of learning first 50 words, although it is difficult for children of this age to examine possible hypotheses systematically. Second, some findings (Haryu, 1996; Smith et al., 1996) suggest that the use of principles in early word learning is not accesible to deliberate control. These facts lead me to assume that infants are born, not with some concrete beliefs about word meanings, but with some constrained mechanism that guides infant's learning the principles about word meanings.
