In this study, we investigate the discourse-functional properties of the extended intransitive clause (EIC) in relation to other clause types in three Formosan languages: Tsou, Kavalan, and Squliq. We offer evidence, based on tracking behavior of NPs, to show that case-marking in EICs is motivated by a core/oblique distinction, and that the core/oblique distinction arises in a systematic way from recurrent patterns in discourse. The referents of the oblique-marked argument nominals in EICs in these languages are shown to be consistently much less likely to be tracked or to be continuous than either the nominative or the ergative argument of a nonactor voice clause. The data derived from investigating the tracking behavior of noun phrases suggest that the validity of a grammatical transitive/intransitive distinction in these languages is quite robust, and that the distinction can best be correctly discerned by examining the functioning of various argument nominals in discourse.