Animacy is a grammatical category, usually of nouns, which influences the form a verb takes when it is associated with that noun.

Usually, animacy has to do with how alive or how sentient a noun is. Humans, for instance, usually occupy a very high slot in an animacy hierarchy, only ever being ranked below deities or gods. Objects such as stones or grass may be ranked very low, and animals usually occupy a space in between; however, according to the spiritual beliefs of the people whose language possesses an animacy hierarchy, certain types of animal or plant may be ranked very highly in the hierarchy.

Examples of languages which possess animacy hierarchies include the Mexican language Totonac and the Apachean languages (such as Western Apache and Navajo), whose animacy hierarchy has been the subject of intense study. Tamil language has a dichotomy of nouns based on animacy.

Apachean example

Like most Athabaskan languages, Apachean languages show various levels of animacy in its grammar, with certain nouns taking specific verb forms according to their rank in this animacy hierarchy. For instance, Navajo nouns can be ranked by animacy on a continuum from most animate (a human) to least animate (an abstraction) (Young & Morgan 1987: 65-66):

Human - - Infant/Big Animal - - Med-size Animal - - Small Animal - - Natural Force - - Abstraction

Generally, the most animate noun in a sentence must occur first while the noun with lesser animacy occurs second. If both nouns are equal in animacy, then either noun can occur in the first position. So, both example sentences (1) and (2) are correct. The yi- prefix on the verb indicates that the 1st noun is the subject and bi- indicates that the 2nd noun is the subject.

(1)	Ashkii	at'ééd	yiníł'į́.
	boy	girl	yi-look
	'The boy is looking at the girl.'

(2)	At'ééd	ashkii	biníł'į́.
	girl	boy	bi-look
	'The girl is being looked at by the boy.'

But example sentence (3) sounds wrong to most Navajo speakers because the less animate noun occurs before the more animate noun:

(3)	* Tsídii	at'ééd	yishtąsh.
	bird	girl	yi-pecked
	'The bird pecked the girl.'

In order express this idea, the more animate noun must occur first, as in sentence (4):

(4)	At'ééd	tsídii	bishtąsh.
	girl	bird	bi-pecked
	'The girl was pecked by the bird.'

Two papers on Navajo animacy:

• Frishberg, Nancy. (1972). Navajo object markers and the great chain of being. In J. Kimball (Ed.), Syntax and semantics, (Vol. 1), (p. 259-266). New York: Seminar Press.
• Hale, Kenneth L. (1973). A note on subject-object inversion in Navajo. In B. B. Kachru, R. B. Lees, Y. Malkiel, A. Pietrangeli, & S. Saporta (Eds.), Issuse in linguistics: Papers in honor of Henry and Renée Kahane, (p. 300-309). Urbana: University of Illinois Press.