A newly emerging view of concept structure, the concepts-in-theories v
iew, suggests that adult concepts are intrinsic mixes of two different
sorts of relations: (a) those involving domain-general tabulations of
frequencies and correlations and (b) those involving domain-specific
patterns of explanation. Empirical results from early cognitive develo
pment suggest that, by the time first words are acquired, most concept
s have this intrinsic mix even though changes in the nature of the mix
can produce marked developmental changes in apparent concepts, word m
eanings, and their use. The concepts-in-theories view suggests that th
e sorts of constraints needed to model the representation and acquisit
ion of concepts cannot be based solely on either perceptual or grammat
ical bases; they must also arise from biases given by specific pattern
s of explanation, patterns that may depart from standard notions of in
tuitive theories. These in turn suggest different views of possible co
nstraints on the acquisition of word meaning.