In this paper, I will claim that switch-reference marking in Mbyá has several modes of use, which require different kinds of description. Specifically, I claim that there is an unmarked mode of use that has a grammatical ("internal") description, as well as other, marked modes of use that require extragrammatical ("external") descriptions. Among phenomena with such marked and unmarked modes, we can further distinguish at least two subtypes: on-call phenomena and fair-weather phenomena; Mybá switch-reference marking is of the latter type.
Dooley, Robert A.
"Switch reference in Mbyá Guaraní: A fair-weather phenomenon,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 33, Article 4.
Available at: https://commons.und.edu/sil-work-papers/vol33/iss1/4