Semantic noun classes in Emai, an Edoid language of Nigeria, are examined with respect to a process of Reference Point Marking (RPM) in order to explore the relationship between discourse and lexical semantics. Across pre- and post-verbal positions subcategorized by verbs like "rere" ("to be far"), these classes are shown to attract RPM in a variable manner. To describe this variability, it proves useful to recognize a spatial stability continuum ranging across and within nouns of place and nonplace, as well as two constraints. For constructions combining place and nonplace nouns, RPM affects the latter, irrespective of its position. For constructions combining exclusively place or nonplace nouns, RPM affects not only nonplace nouns in post-verbal position but the pre-verbal noun when the spatial position of its referent represents new information in discourse. Finally, through apparent irregularities in their application, these constraints on discourse form and lexical semantics are shown to interlock with assumptions of spatial stability differentially assigned to nominals functioning as Figure or Ground. (Author/MSE)