Using LFG a-structure to determine the subcategorization frames of Setswana verbs

The verb lexicon, and more specifically verb subcategorization frames, forms an integral part of any computational grammar. In building a Lexical Functional Grammar (LFG) computational grammar for Setswana, it is therefore necessary to determine, in a principled way, the subcategorization frames for both basic verb roots as well as extended verb roots since verbal extension is a productive process in Setswana. Sequences of verbal extensions are not uncommon. In this article we investigate how four common extensions, viz. the causative, applicative, reciprocal and passive, each change the LFG argument structure of a basic verb root that they extend. We also consider what the subcategorization frame of the newly extended verb root is by applying lexical mapping theory (LMT). Due to the compositionality of the meaning of verbal extensions, we are able to generalise our results to sequences of extensions with the purpose of determining their subcategorization frames.