The count/mass disinction is often considered to be a semantic one because it distinguishes those nouns that refer to countable things from those that refer to non-countable things. However, exceptions indicate that semantic properties alone are not sufficient to determine noun sub-categorization. Therefore, such sub-categorization must be defined syntactically for the mature language user. This syntactic definition is couched in terms of distributional properties such as privileges of occurrence within a set of syntactic contexts. Membership within a category or subcategory is defined over a set of linguistic environments into which lexical insertion of that category is permissible. The acquisition of a set of selection rules on quantifiers is examined that invokes the count/mass distinction and serves to partially define the distinction itself from a syntactic distributional viewpoint. Results of an experiment are presented that suggest certain overgeneralizations over this set of syntactic contexts. The results illustrate that in acquiring the count/mass distinction, children must learn that: (1) mass nouns may not be pluralized; (2) certain quantifiers exclusively select for either count or mass nouns; and (3) certain quantifiers take singular count nouns even though plural quantities are being referred to. (Author/JK)