This paper discusses three constraints on word meaning in early language acquisition: the whole-object assumption, the taxonomic assumption and the mutual exclusivity assumption. Seen the importance of word learning, children might be assumed to collect all possible sources of information to restrict a word's meaning, including information given by grammatical form class and the pragmatics of the situation. Word-learning constraints interact with constraints of other sources of information, but they can also be a particularly useful source of information for children who have not yet mastered grammatical form class.