When (not) to use the Japanese particle wa: Groundhood, contrastive topics, and grammatical functions

In Japanese linguistics and elsewhere, the particle wa in its thematic use has been widely regarded as a paradigmatic instance of a 'topic marker'. This work aims to demonstrate that, contrary to this received wisdom, most often thematic wa merely indicates the groundhood (the status as a nonfocus) rather than the topichood (the status as a topic) of the marked constituent, although it serves as a marker of contrastive topic in some configurations. In a root clause, as a rule, an explicit argument must be marked by thematic wa if it (i) is nonfocal and (ii) does not cooccur with an explicit, nonfocal sister argument less oblique than it. This implies that an explicit, nonfocal subject must be wa-marked, given that a subject is by definition the least oblique argument. Arguments marked by thematic wa despite not meeting this condition (e.g. a wa-marked object cooccurring with a wa-marked subject), as well as at least some instances of wa-marked adjuncts, are interpreted as contrastive topics. It is further pointed out, based on corpus data, that it is much more common for wa to indicate mere groundhood than topichood.