The nominative case particle ga in Japanese cannot be dropped when the expression it marks is focused, i.e., when the expression it marks is interpreted as contrasting with some other object(s) of the same type. This simple constraint, in conjunction with a theory of the interaction between focus and intonation, automatically accounts for several facts about ga-ellipsis that have hitherto been subjected to various misinterpretations, including (i) the fact that ga appears to be harder to drop when it marks an unergative subject than when it marks an unaccusative subject and (ii) the fact that ga is harder to drop when it is not adjacent to a predicate. The results of two questionnaire surveys, in which I obtained acceptability judgments from a relatively large number of speakers, will be shown to support the proposed account.
(S. Yatabe, "Particle ellipsis and focus projection in Japanese," in Language, Information, Text, Vol. 6, Department of Language and Information Sciences, University of Tokyo, 1999, pp. 79-104.)