Emergence of optional accusative case marking in Khoe languages

A number of languages of the Khoe family – one of three genetic lineages comprising south-
ern African Khoisan – show an accusative marker, typically a postposition which in its
elsewhere form has the shape (-)(ʔ)à. In all languages for which adequate data is available,
this postposition is optional on object NPs, at least in some circumstances. A few proposals
have been made for the grammaticalisation of this marker, notably by Kilian-Hatz (2008: 55;
2013: 376–378). However, not only are these proposals specific to the Khwe language, but
also they fail to account for the fact that (-)(ʔ)à marks the accusative and that it is optional.
In this paper I widen the net to the Khoe family as a whole, and consider the synchronic sit-
uations for the usage of the marker (-)(ʔ)à and its putative cognates in those languages for
which pertinent data is available. This is used to motivate a diachronic proposal concern-
ing the grammaticalisation of (-)(ʔ)à in the modern languages. Specifically, it is proposed
that the accusative marker began life as a presentative copula; this served to index an item,
drawing the addressee’s attention to it. It later became an optional accusative marker via
grammaticalisation processes akin to those outlined in McGregor (2008; 2010; 2013; 2017)
for the development of optional ergative case markers in some Australian languages. Thus
the grammaticalisation scenario proposed is consistent with pathways of development of
other optional case-markers.