Hard Words

How do children acquire the meaning of words? And why are words such as know harder for learners to acquire than words such as dog or jump? We suggest that the chief limiting factor in acquiring the vocabulary of natural languages consists not in overcoming conceptual difficulties with abstract word meanings but rather in mapping these meanings onto their corresponding lexical forms. This opening premise of our position, while controversial, is shared with some prior approaches. The present discussion moves forward from there to a detailed proposal for how the mapping problem for the lexicon is solved, as well as a presentation of experimental findings that support this account. We describe an overlapping series of steps through which novices move in representing the lexical forms and phrase structures of the exposure language, a probabilistic multiple-cue learning process known as syntactic bootstrapping. The machinery is set in motion by word-to-world pairing, a procedure available to novices from the onset, one that is efficient for a stock of lexical items (mostly nouns) that express concrete basic-level concepts. Armed with this foundational stock of "easy" words, learners achieve further lexical knowledge by an arm-over-arm process in which successively more sophisticated representations of linguistic structure are built. Lexical learning can thereby proceed by adding structure-to-world mapping methods to the earlier available machinery, enabling efficient learning of abstract items-the "hard" words. Thus acquisition of the lexicon and the clause-level syntax are interlocked throughout their course, rather than being distinct and separable parts of language learning. We concentrate detailed attention on two main questions. The first is how syntactic information, seemingly so limited, can affect word learning so pervasively. The second is how multiple sources of information converge to solve lexical learning problems for two types of verbs that pose principled obstacles for word-to-world mapping procedures. These types are perspective verbs (e.g., chase and flee) and credal verbs (e.g., think and know). As we discuss in closing, the outcome of the hypothesized learning procedure is a highly lexicalized grammar whose usefulness does not end with successful acquisition of the lexicon. Rather, these detailed and highly structured lexical representations serve the purposes of the incremental multiple-cue processing machinery by which people produce speech and parse the speech that they hear.