An antipassive construction involves a verb that is semantically transitive, but syntactically intransitive (derived detransitivized verb). From a semantic perspective, the verb has two arguments, but its semantic object (patient) has been syntactically demoted (or deranked).[1] There are two types of antipassive object demotion:

1. oblique subtype: the patient appears in an oblique form (oblique case and/or with an adposition) instead of in its typical form (accusative or absolutive)
2. implicit subtype: the patient cannot be expressed at all

Antipassive constructions appear most often in ergative languages, as an alternative to the ergative construction. The part of the sentence that appears in ergative form in an ergative construction appears in absolutive case in an antipassive construction, while the part of the sentence that appears in absolutive form in an ergative construction appears instead in oblique form or not at all in an antipassive construction. In languages that feature agreement between a verb and its arguments, the verb of an antipassive construction can only display agreement with whichever argument appears in absolutive form.

Verbs of antipassive constructions appear in a morphologically distinct form than their transitive equivalents. Strategies include the use of an antipassivizing derivational morpheme specific to this function or a syncretic derivational morpheme that has other functions as well[2]. In some languages, multiple such morphemes exist, sometimes even appearing simultaneously. In other languages, the only sign of an antipassive construction is in the change in verbal agreement.

The productivity of the antipassive differs across languages; in some, it is fully productive (an antipassive construction can be formed from any transitive verb), while in others it may be partially productive (limited to transitive verbs of a certain type or meaning) or not productive at all (limited to a closed class of transitive verbs). The degree of productivity of this construction does not appear in the parameter values, but may be noted in the commentary. The grammatical environment or semantic function in which the antipassive is used, is another feature that need not be considered in assigning parameter values, since languages differ greatly in this respect.

Types:

NoAntipass: The language does not have antipassive constructions.

AntipassObq: Antipassive constructions feature the semantic object of the verb in an oblique form (oblique case and/or with an adposition).

AntipassImpl: Antipassive constructions do not feature the semantic object of the verb.

NoAntipassAgr: Antipassive constructions do not feature any kind of agreement on the verb.

AntipassAgrErg: In an antipassive construction, the verb uses the same strategy to mark agreement with the argument appearing in absolutive form as it would with the agent in ergative form in an ergative construction.[3]

AntipassAgrAbs: In an antipassive construction, the verb uses the same strategy to mark agreement with the argument appearing in absolutive form as it would with the patient in absolutive form in an ergative construction.[4]

The values AntipassObq and AntipassImpl may each appear alongside any of the other parameter values listed, separated by a plus sign (+).

[1] This should not be confused with the passive construction, in which it is the agent that is demoted.

[2] These functions may include “detransitivizing” a verb, making it reflexive, or changing its tense, aspect, or mood.

[3] This is only possible if such agreement exist in the ergative construction. If this value applies, examples should be provided in the commentary.

[4] This is only possible if such agreement exist in the ergative construction. If this value applies, examples should be provided in the commentary.