Labile verb

In general linguistics, a labile verb (or ergative verb) is a verb that can be either transitive or intransitive, and whose subject when intransitive corresponds to its direct object when transitive. Labile verbs are a prominent feature of English, but they also occur in many other languages.
Terminology.
The terminology in general linguistics is not stable yet. Labile verbs can also be called "S=O-ambitransitive" (following R.M.W. Dixon's usage), or "ergative", following Lyons's influential textbook from 1968. However, the term "ergative verb" has also been used for unaccusative verbs, and in most other contexts, it is used for ergative constructions.
Labile verbs in English.
In English, most verbs can be used intransitively, but ordinarily this does not change the role of the subject; consider, for example, "He ate the soup" (transitive) and "He ate" (intransitive), where the only difference is that the latter does not specify what was eaten. By contrast, with a labile verb the role of the subject changes; consider "it broke the window" (transitive) and "the window broke" (intransitive).
Labile verbs can be divided into several categories:
Some of these can be used intransitively in either sense: "I'm cooking the pasta" is fairly synonymous with both "The pasta is cooking" (as an ergative verb) and "I'm cooking", although it obviously gives more information than either.
Unlike a passive verb, a nominalization, an infinitive, or a gerund, which would allow the agent to be deleted but would also allow it to be included, the intransitive version of a labile verb normally requires the agent to be deleted:
Indeed, the intransitive form of a labile verb can be used to suggest that there is no agent. With some non-labile verbs, this can also be achieved using the reflexive voice:
This use of the reflexive voice can be used to indicate the lack of any agent, but it can also be used in cases when a specific agent is unknown. For example, the phrases "John broke the window, or maybe Jack did — at any rate, the window broke" and "John solved the problem, or maybe Jack did — at any rate, the problem was solved" both have quite naturally understandable meanings, though they're slightly idiomatic.
Another way to construct the reflexive voice is:
This use of the reflexive voice indicates that the subject of the sentence "is" the causative agent; the phrase "John solved the problem, or maybe Jack did — at any rate, the problem solved itself" is literally self-contradictory, though idiomatic usage does not always follow this prescription. Accordingly, some grammarians would consider both "The window broke" and "The problem solved itself" to be examples of a distinct voice, the middle voice.
The significance of the labile verb is that it enables a writer or speaker not only to suppress the identity of the outside agent responsible for the particular process, but also to represent the affected party as in some way causing the action by which it is affected. This can be done neutrally when the affected party can be considered an institution or corporate entity and the individual member responsible for the action is unimportant, for example "the shop closed for the day". It can also be used by journalists sympathetic to a particular causative agent and wishing to avoid assigning blame, as in "Eight factories have closed this year."
In Norwegian.
The labile verbs in Norwegian have one conjugation pattern for when the verb is transitive and another one for when the verb is intransitive:
In French.
French is another language that has them, developed from lack of distinguished sense in Gallo-Roman Vulgar Latin:
However, note that the use of the reflexive form of the verb to express the anticausative meaning is more common.
Further, verbs analogous to English "cook" have even more possibilities, even allowing a causative construction to substitute for the transitive form of the verb:
In Dutch.
In Dutch, labile verbs are used in a way similar to English, but they stand out as more distinct particularly in the perfect tenses.
In the present, the usage in both languages is similar, for example:
However, there are cases where the two languages deviate. For example, the verb "zinken" (to sink) cannot be used transitively, nor the verb "openen" (to open) intransitively:
and
In this last case, one could say: "De deur gaat open." (lit. "The door goes open"), while the former would be stated as "De marine liet het schip zinken." (lit. "The navy let the ship sink").
A difference between Dutch and English is that typically the perfect tenses of intransitives take "zijn" (to be) as their auxiliary rather than "hebben" (to have), and this extends to these verbs as well. 
Perfect labile innocence.
Labiles are verbs of innocence, because they imply the "absence" of an actor who could possibly be blamed. This association is quite strong in Dutch and speakers tend to treat verbs such as "forgetting" and "losing" as ergatives in the perfect tenses even though they typically have a direct object and are really transitive verbs. It is not unusual to hear sentences such as:
Something similar happens with compound verbs such as "gewaarworden" ('become aware (of something)'). It is a separable compound of "worden" ('become'), which is a typical 'process'-verb. It is usually considered a copula, rather than an ergative, but these two group of verbs are related. For example, copulas usually take "to be" in the perfect as well. A verb such as "blijven" ('stay') is used both as a copula and as an ergative and all its compounds ("nablijven" ('stay behind'), "bijblijven" ('keep up'), "aanblijven" ('stay on') etc.) are ergatives.
"Gewaarworden" can take two objects, a reflexive indirect one and one that could be called a "causative object". In many languages the causative object would take a case such as the genitive, but in Dutch this is no longer the case:
The perfect usually takes "to be" regardless of the objects:
In Hebrew.
Hebrew does have a few labile verbs, due in part to calques from other languages; nonetheless, it has fewer labile verbs than English, in part because it has a fairly productive causative construction and partly distinct mediopassive constructions. For example, the verbs (active) and (its mediopassive counterpart) both mean "to break", but the former is transitive (as in "He broke the window") and the latter is intransitive (as in "The window broke"). Similarly, the verbs (active) and (its causative counterpart) both mean "to pass", but the former is intransitive (as in "He passed by Susan") and the latter is transitive (as in "He passed the salt to Susan")