Investigations into the semantics of the spatial and non-spatial uses of in and on have tended to assume that a type-level similarity exists between these two prepositions. However, their syntactic distributions, while overlapping, are not equal in scope (Navarro, 1998). In this paper, we ask whether these distributional differences might be related to semantic differences between the two terms. The preliminary evidence collected here suggests that in and on have slightly different levels of interpretability, even in their prepositional uses. Thus, both semantically and syntactically, the assumption of type-level similarity may need to be qualified.