We describe a theoretical investigation into the semantic space described by our interlingua (IL), which currently has 191 main verb classes divided into 434 subclasses, represented by 237 distinct Lexical Conceptual Structures (LCSs). Using the model of aspect in Olsen (1994b, 1997a)---monotonic aspectual composition---we have identified 71 aspectually basic subclasses that are associated with one or more of 68 aspectually non-basic classes via some lexical (``type-shifting'') rule (Bresnan 1982, Pinker 1984, Levin and Rappaport Hovav 1995). This allows us to refine the IL and address certain computational and theoretical issues at the same time. (1)

From a linguistic viewpoint, the expected benefits include a refinement of the aspectual model in (Olsen:1994b, 1997a) (which provides necessary but not sufficient conditions for aspectual composition), and a refinement of the verb classifications in (Levin 1993); we also expect our approach to eventually produce a systematic definition (in terms of LCSs and compositional operations) of the precise meaning components responsible for Levin's classification. (2) Computationally, the lexicon is made more compact. Also cross-referenced as UMIACS-TR-97-86 Also cross-referenced as LAMP-TR-012