From the introduction, "In Cheyenne, as in other Algonquian languages, when two or more third-person nominals are in the same sentence or "contextual span" (Wolfart 1973:17), one of the nominals must be treated as "nearer" or more "in focus" than the other third-person nominal(s). The nearer person is called the "proximate" form while any other(s) is said to be "obviate" (sometimes called a "fourth-person"). The proximate nominal can function as the "topic" of a discourse segment, or "the person earlier spoken of and already known" (Bloomfield 1962:38). The marking of one or more nominals as obviates is called "obviation".
Leman, Wayne E.
"Remarks on Cheyenne obviation and pluralization,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 21, Article 5.
Available at: https://commons.und.edu/sil-work-papers/vol21/iss1/5