How do children learn the meanings of number words like "one," "two," and "three"? Whereas many words that children learn in early acquisition denote individual things and their properties (e.g., cats, colors, shapes), numerals, like quantifiers, denote the properties of sets. Unlike quantifiers such as "several" and "many," numerals denote precise quantities. Further, numerals form an unbounded list and denote a potentially infinite set of quantities. On these grounds, they would appear to constitute a unique learning problem to children acquiring language, quite distinct from the problem of learning nouns or verbs. Despite these important differences between numerals and other words, researchers such as Syrett, Musolino, and Gelman (this issue) have converged on the idea that some of the more difficult problems that they pose in acquisition might be explained by previously attested word learning mechanisms. Previous studies have brought into question whether specialized domain-specific mechanisms are required to explain number word learning and raise the possibility of the idea that numerals are more similar to other words than sometimes supposed. The case of syntactic bootstrapping has received particular attention in recent years yet has been accompanied by relatively little experimental evidence. The goal of the study by Syrett et al. was to differentiate several possible theories of how syntactic cues might constrain number word acquisition. For the sake of this discussion, Barner will distinguish between three distinct syntactic bootstrapping accounts. On one view, children might learn that number words denote precise numerosities by attending to specific constructions in which they are used that logically entail aspects of their lexical meaning. On this view, a single syntactic contrast could allow children to form their first exact numerical meaning, on analogy with the indefinite determine "a." On a second view, children might use syntactic bootstrapping to discover that numerals denote the properties of sets but not precise numerosities "per se." For example, they could notice that numerals such as "one," "two," and "three" are used in similar syntactic frames as quantifiers such as "several," "many," and "all." Finally, a third view, which Syrett et al. lay out, is that children might detect both that numerals denote properties of sets and that they denote precise quantities by attending to the syntactic frames in which they are used. By this view, the particular combination of syntactic frames in which only numbers occur might signal that their meanings are unlike any other quantifier, and that only they denote precise quantities. (Contains 2 footnotes.)