Preverbs are positionally-delimited grammatical forms that remain understudied. We examine their semantic classes in West Benue Congo (WBC) and its minor language Emai, which until recently was undocumented. Preverb classes in Emai display a subset of semantic categories identified in Dixon (1991, 2006, 2010) and Nuyts (2001, 2005, 2006, 2016). There are eight semantic classes for 30 odd preverb forms. They are apportioned according to their qualitative or quantitative character. Preverbs do not include traditional auxiliary categories of aspect, tense, and modality, which exhibit distinct diachronic and synchronic character. Common to preverbs is their orientation to grammatical subject, rather than utterance speaker. Members of each class ascribe a property to clausal subject. Preliminary evidence suggests that preverbs of similar semantic character exist in other West African languages.