Ambitransitive verb

An ambitransitive verb is a verb that can be intransitive or transitive without requiring a morphological change. That is, the same verb form may or may not require a direct object. English has a large number of ambitransitive verbs. Examples include read, break, and understand (e.g., "I read the book," saying what was read, or just "I read all afternoon").

Ambitransitive verbs are common in some languages, and much less so in other languages, where valency tends to be fixed, and there are explicit valency-changing operations (such as passive voice, antipassive voice, applicatives, causatives, etc.).

Agentive and patientive

Generally speaking, there are two types of ambitransitive verbs, distinguished by the alignment of the semantic roles of their arguments with their syntactic roles.

Agentive

Agentive (S = A) ambitransitives are those where the single argument of the intransitive (S) is agentive and it corresponds to the agent (A) of the transitive. In Mary (S) is knitting, and Mary (A) is knitting a scarf (O), the person doing the knitting in both sentences is Mary. Likely candidates for this type of ambitransitive include those where an action can be described in general terms or with respect to a specific patient. English examples include eat, follow, help, knit, read, try, watch, win, know, and many others. These transitive versions have been called unergative verbs, but this term is not fully accepted since it is used for many other senses.