Within linguistics, obviative (abbreviated OBV) third person is a grammatical-person marking that distinguishes a referent that is less important to the discourse from one that is more important (proximate). The obviative is sometimes referred to as the "fourth person".

In English and many 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 dog" is ambiguous: it could mean that she saw her own dog or that she saw someone else's dog. This is because it is not clear, in some contexts, if "she" and "her" refer to the same person.

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 to distinguish between the two.

For example, in the sentence "the quick brown fox jumps over the lazy dog", there are two third-person referents, the fox and the dog. Thus, 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 jumps-PROX>OBV over 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 jumps-OBV>PROX over 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", and 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 occurs also in some Salishan languages and in the language isolate Kutenai as well as in the more southern Keresan languages.

Obviative markers are used in Africa in some Nilo-Saharan and Niger–Congo languages.