Obviative (abbreviated OBV) third person is a grammatical-person marking that distinguishes a non-salient (obviative) third-person referent from a more salient (proximate) third-person referent in a given discourse context. The obviative is sometimes referred to as the "fourth person".
Comparison with other grammatical-person marking systems
In English and other European languages, the principal means of distinguishing between multiple third-person referents is using gender or (lack of) reflexive. Thus, in "she saw him" it is clear that there are two third persons because they are of different genders; in "she saw her" it is clear that there are two third persons because otherwise one would say "she saw herself". However, "she saw her mother" is ambiguous: it could mean she saw her own mother, or it could mean she saw someone else's mother.
An obviative/proximate system has a different way of distinguishing between multiple third-person referents. When there is more than one third person named in a sentence or discourse context, the most important, salient, or topical is marked as "proximate" and any other, less salient entities are marked as "obviative." Subsequent sentences that refer to previously-named entities with pronouns or verbal inflections can then use the proximate and obviative references that have already been established in order to distinguish between the two.
For example, in the sentence "the quick brown fox jumped over the lazy dog," there are two third-person referents, the fox and the dog. So one of them has to be proximate and the other one has to be obviative, depending on which one the speaker considers more central to the story. If the fox is the more important one, the sentence might look something like "the quick brown fox-PROX jumped-PROX>OBV the lazy dog-OBV," where PROX>OBV is verbal inflection indicating a proximate subject acting on an obviative object. In that case, a subsequent sentence "and then PROX went-PROX away" would mean that the fox went away.
On the other hand, if the dog is the more important one, the sentence might look something like "the quick brown fox-OBV jumped-OBV>PROX the lazy dog-PROX," where OBV>PROX is verbal inflection indicating an obviative subject acting on a proximate object. In that case, the same subsequent sentence "and then PROX went-PROX away" would mean instead that the dog went away. By contrast, an equivalent subsequent sentence in English, such as "and then he went away," would not necessarily indicate whether "he" is the fox or the dog.
An analogy that has been used to explain obviation is that the proximate is the entity in the "spotlight" while any other, obviative entities are out of the spotlight or "hangers-on."
Obviate/proximate distinctions are common in some indigenous language families in northern North America. Algonquian languages are perhaps best known for obviation, but the feature also occurs in some Salishan languages and in the language isolate Kutenai, as well as in the more southern Keresan languages.
- Where animacy is involved, animate noun phrases tend to be proximate, while inanimate noun phrases tend to be obviative.
- Possessors are frequently obligatorily proximate and possessees are thus obligatorily obviative.
- Obviation is most common in head-marking languages since the obviative is useful in disambiguating otherwise unmarked nominals.
- The obviative referent seems to always be the marked form, while the proximate is unmarked.
- Obviative marking tends to apply only to the third person, though it has been attested in the second person in a handful of Nilo-Saharan languages.
- Proximate/Obviative assignments are preserved throughout clauses and are also often constant over longer discourse segments.
Notable language-specific examples
The following is a typical example of obviate/proximate morphology in the Eastern dialect of the Algonquian Ojibwe language, in which the obviative is marked on nouns and demonstratives and reflected in pronominal verb affixes:
Maaba dash shkinwe wgii-bwaadaa wii-bi-yaanid myagi-nishnaaben waa-bi-nsigwaajin maaba dash oshkinawe o-gii-bawaad-am-n wii-bi-ayaa-ini-d mayagi-nishanaabe-an x-wii-bi-nis-igo-waa-d-in this EMP young.man 3-PAST-dream-3INAN-OBV FUT-coming-be.at-OBV-3 foreign-people-OBV REL-FUT-coming-kill-INV-3-OBV
'Then this (PROX) young man (PROX) dreamed (PROX) that foreigners (OBV) would come (OBV) to kill (OBV) them (PROX).'
Note that this example shows that the proximate referent need not necessarily be the subject of a clause.
Potawatomi (an Algonquian Language) is notable for having two degrees of obviation, known as "obviation" and "further obviation". Note that "further obviation" is rare, but when it does occur, a "further obviative" referent deemed even less salient than the obviative referent can be marked by an additional obviative suffix. The following is the sole example to appear in the literature on Potawatomi:
ktokmamnannun our (12) chief(s) (3″) 
Charles Hockett did posit the following example, but he never checked it to see if it is was grammatical:
waposo waposo-n waposo-n-un rabbit rabbit-OBV rabbit-OBV-OBV /proximate/ /obviative/ /further obviative/ 
Obviation in the Ingush language, a heavily dependent-marking language, is an exception to the generalization that the obviative occurs in head-marking languages. Obviation is not overtly marked in Ingush, but is implied by the fact that certain constructions are only possible when one referent has salience over another.
For example, if a non-subject-referent has salience over the subject and precedes the other co-referent, reflexivization (normally used only when there is a coreferent to the subject) is possible. This is shown in the example below where the non-subject-referent appears to have salience over the subject:
Muusaajna shii zhwalii t'y-weaxar Musa-DAT 3S-RFL-GEN dog on-bark-WITNESSED PAST
'Musa's dog barked at him.'
If the subject is salient ("proximate"), on the other hand, the subject's possessor may not antecede the third-person object, and the possession must be indirectly implicated as follows:
Muusaa siesaguo liex Musa wife-ERG seek
'Musa's wife is looking for him.' (Lit. 'The wife is looking for Musa.')
- Kibort, Anna. "Person." Grammatical Features. 7 January 2008.  Retrieved on 2009-10-25.
- "Spec Tech: Wait, who hit who?". February 17, 2011. Retrieved April 7, 2015.
- Quinn, Conor McDonough (2006). "Algonquian grammar without all the grammar." (PDF). Retrieved April 7, 2015.
- Mithun, Marianne. The languages of Native North America. 76-68.
- Gregersen, Edgar A. Language in Africa: an introductory survey. New York: Gordon and Breach Science Publishers Inc, 1977. 51-52.
- "The Scientific Interest of Ingush - Section 5, Obviation" University of California, Berkeley (Unpublished).  Retrieved on 2009-10-29.
- Hockett, Charles. Potawatomi II: Derivation, Person Prefixes, and Nouns. International Journal of American Linguistics. 1948. 14:63-74.
- Hockett, Charles. What Algonquian is Really Like. International Journal of American Linguistics. 1966. 32:59-73.
- Schlenker, Philippe. Propositional Attitudes and Indexicality: A Cross-Categorial Approach. University of Southern California, 1994. 44-45.
- 7. Aissen, Judith. 1997. On the syntax of obviation. Language 73:4.705-50.