Abstract
A common assumption underlying the semantic feature and the functional core hypotheses of lexical development is that attributes abstracted from the referents of a word are sufficient to determine the extension of that word. The present paper begins by challenging this assumption. A contrastive hypothesis is instead advanced to explain the early lexical development of children, and the predictions of this hypothesis are shown to be consistent with available data on overextension. The paper concludes with a critical discussion of the semantic feature and the functional core hypotheses in which it is shown that neither of these hypotheses can account for the data on overextension.