A study explored the functionalist-constructivist approach to acquisition of grammar where word classes emerge as a result of distributional differences related to function. Focus is on acquisition of two Swedish forms, "i" and "pa," which can belong to the categories of either particles or prepositions, in two Swedish children, based on longitudinal corpus data. It was predicted that uses of the two forms with the same basic function (locative or directional) would not be acquired simultaneously as prepositions and particles, and that spatial uses of the forms would be acquired before non-spatial uses. Overall, results failed to confirm these predictions. Data for only one child and one form seemed to confirm both predictions. Both children showed no difficulty in acquiring non-spatial uses of "pa" simultaneously with or even before the spatial ones. Three experiments then tested (1) whether preposition and particle usages could be classified based on simple distributional data only, (2) whether consideration of stress patterns facilitated this analysis, and (3) a hypothesized conceptual structure for mapping acquisition. Results lent some support to the functionalist-constructivist approach to acquisition of word classes. Contains 24 references. (MSE)