Starting at about 18 months of age, children become remarkably capable of learning the vocabulary of natural languages. Yet word learning presents a problem of induction that must somehow be solved by such very young children, with their limited information processing abilities. In order for children to acquire language as rapidly as they do, they must have biases that enable them to rule out many alternative hypotheses for the meanings of a word and that lead them instead to focus on hypotheses that are reasonably likely to be correct (Markman, 1989; Markman & Hutchinson, 1984; Markman & Wachtel, 1988). A sophisticated, intelligent adult, let alone a 2-year-old, would never be able to settle on the meaning of a word by open-mindedly considering every possible hypothesis and waiting for evidence that would rule out all but one (Quine, 1960). It has been suggested that children use several assumptions to solve the inductive problem posed by word learning; among these are the whole-object assumption, the taxonomic assumption, and the assumption of mutual exclusivity. In this chapter, I will review some of the evidence that children rely on these assumptions to guide their initial hypotheses about what words mean and will try to reconcile this argument with some conflicting evidence about whether these constraints are available to young children just starting to acquire language.

The taxonomic and whole-object assumptions

When an adult points to an object and labels it, the novel term could refer to an object category, but it could also refer to a part of the object or to its substance, color, or weight, and so on.