Most people are familiar with the passive voice, largely from instructions to avoid using it. Usually, it's presented thusly: a sentence may be in the active voice or the passive. For instance, compare the following:
[1] i. Joanne drank the wine
ii. The wine was drunk by Joanne
Both sentences mean the same thing; in each one, Joanne plays the semantic role of agent, and the wine is the patient. That is to say, in both sentences Joanne is the one doing the drinking, and the wine is what gets drunk. In a sentence in the active voice like (i), then, the agent is normally the sentence's subject, while the patient is the direct object. On the other hand, in the passive voice, the patient (remember, that's the entity that the action is being done to) is normally the subject, while the agent is the object of a preposition, by — that is, if it's not omitted entirely, which is possible in passive sentences but not in active ones — The wine was drunk is a perfectly adequate sentence, while *Drunk the wine clearly is not.
The verb changes, too. The main verb in both the active and passive sentences is drink, but notice that it takes different forms. In the active sentence, it's drank, in the preterit (or simple past) tense, while in the passive sentence, it's drunk, which is the past participle of drink. It's accompanied by an auxiliary verb, was, a form of be. So that's what you do to make an active sentence into a passive: switch the verb to the past participle form and add a form of be as its auxiliary, switch the direct object into the subject position, and slide the subject into a prepositional phrase (or just drop it). Of course, this is only a rough overview, but it summarizes the most common differences between the active and passive voices.
The get-passive
As I mentioned, the construction usually referred to as the passive uses a form of be as an auxiliary verb. But that's actually not the only way to form the passive voice in English. Equally common is the "get-passive", which uses a form of get as the auxiliary verb. Let's look an example:
[2] i. A cougar attacked Kim
ii. Kim was attacked by a cougar
iii. Kim got attacked by a cougar
This example illustrates all three forms: (i) is in the active voice, (ii) is the "be-passive", and (iii) is the get-passive. The two passive forms are pretty similar. Again, you can see that the agent (a cougar) is the subject in the active version, (i), while it's in a prepositional phrase headed by by in both of the passive versions. So the basic form of the get-passive and the be-passive are the same, the exception being the choice of auxiliary verb.
There are some minor syntactical differences, though. While I described get as an auxiliary verb, that's actually an oversimplification. Be, however, is truly an auxiliary verb, which is indicated by certain tests:
[3] i. Was Kim attacked by a cougar?
ii. Kim was not attacked by a cougar
In (i), the subject and verb are inverted — they exchange positions, which is a typical way to form yes-or-no questions in English. This is one of the tests for auxiliary verbs in English: only auxiliary verbs can be inverted in this way; if there is not an auxiliary verb present, a dummy auxiliary must be inserted. (ii) shows a second test — only auxiliary verbs can be negated. If there is not an auxiliary, again a dummy must be used to form a negative. So let's contrast with the get-passive:
[4] ia. *Got Kim attacked by a cougar?
iia. *Kim got not attacked by a cougar
ib. Did Kim get attacked by a cougar?
iib. Kim did not get attacked by a cougar
Notice that when we try to form questions and negatives as in the earlier (3i) and (3ii), the results are ungrammatical — sentences (4ia) and (4iia) are impossible in English. So we see that with the get-passive, you can't invert subject and verb to form a question (4ia), nor can you attach the negation particle, not, to get (4iia). That's because get is not truly an auxiliary verb, though it's used here to perform a similar function. Because it's not an auxiliary verb, it's necessary to attach the dummy auxiliary, do, which then undergoes inversion or negation, as in the fully grammatical examples (4ib) and (4iib).
Semantics of get-passives
Naturally, there are some differences in meaning between get-passives and regular old be-passives. The most obvious difference is one of register, or formality. Be-passives are used in all registers, both in formal and informal speech. The be-passive is particularly typical of some types of formal writing (and it's this heavy use that has caused many style guides to condemn the passive). By contrast, get-passives are typical of casual speech. Go back and compare (2ii) and (2iii) — it's clear that the get-passive is much less formal; it's particularly rare in formal writing.
[5] i. Joe was dressed [by someone]
ii. Joe got dressed
This example illustrates a difference in the way that be-passives and get-passives treat agents and patients. Compare (5i) and (5ii) (ignore the adjectival interpretation of (5i), which is not a passive construction). In both examples, the agent is not explicitly specified, but in (5i) the natural interpretation is that Joe was dressed by another person. In (5ii), by comparison, the natural interpretation is that Joe dressed himself — this is known as a reflexive construction. Get-passives are often used in situations in which the agent and patient are the same entity.
In a similar vein, get-passives are often used in cases where the patient (the subject of the passive sentence) is seen to play a larger role in incurring whatever befell them:
[6] i. Anthony was slapped by Charlotte
ii. Anthony got slapped by Charlotte
The difference is subtle, but in (6ii) it seems likely that Anthony did something to deserve being slapped. This is related to the previous example. In (6ii) Anthony, the patient, was partially the cause of his getting slapped, while in (5ii), Joe was simultaneously agent and patient — and quite obviously it was Joe who caused himself to become clothed. The patient in a get-passive, then, frequently plays a larger role in the action than the patient in a be-passive.
[7] i. Gunfire was heard in the auditorium
ii. *Gunfire got heard in the auditorium
In the first two examples, we see a sentence which is grammatical in the be-passive but ungrammatical in the get-passive. While be-passives can often have non-living entities for their subjects, got-passives do more rarely, and they hardly ever have abstract entities like gunfire as their subjects. Example (7ii) is impossible, as gunfire can't perform an action at all, and certainly can't act in such a way as to cause itself to be heard.
[8] i. The book was torn during the move
ii. The book got torn during the move
iii. Her identity was known
iv. *Her identity got known
Here we see another difference between the be-passive and the got-passive. The be-passive tends to describe events that happened either at an unspecified time or for a period of time. In (8i), the actual moment in which the book was torn is deemphasized. (8ii), in contrast, emphasizes that there was a specific point during the trip in which the book was damaged. The same difference exists between (8iii) and (8iv), except that in this case, (8iv) is ungrammatical, since something isn't generally known only at a specific moment in time. If we use a verb that is punctual — that is, one describing an event at one particular point in time — it becomes more acceptable: Her identity got discovered sounds far more natural. This punctuality underlies a great many of the construction's most common usages.
[9] i. Calvin and Susie were married in 2001
ii. Calvin and Susie got married in 2001
In this case, the second choice is by far the more common, because the emphasis on a particular point in time is particularly useful. The get-passive naturally lends itself to this use; it marks the beginning of the marriage, while the be-passive sounds somewhat stilted in comparison. This last sort of usage, described sometimes as the "actional passive" (as opposed to the "statal passive" that be tends to mark) is actually extended to uses that are not really passive at all:
[10] i. Steve got caught up on his reading
ii. Claire and Suzanne got acquainted
iii. Maria got tired [or cold, or hungry, etc.]
In (10i), it's clear that nothing caught Steve up on his reading — thus, this is not a passive construction at all. (10ii) is also not actually passive, though it may appear that way: nothing about the sentence implies that someone actually "acquainted" the two, and attempting to form an active sentence like *I acquainted Claire and Suzanne sounds bizarre and at the very least quite outdated. In the last example, tired does historically come from a past participle, but in the present language it is used as an adjective. Further, you can replace it with adjectives that clearly never were derived from verbs at all. These last few examples show a blurring between get-passives and predicative constructions — that is, constructions that assign a certain quality to the subject. To illustrate this, try mentally replacing get with become in all the examples we've looked at. Some of them clearly don't work (*Anthony became slapped by Charlotte) and others are awkward but some work quite well. As with many things in language, borders between these categories are fuzzy rather than well-defined.
References
Huddleston, Rodney and Pullum, Geoffrey K., 2005. A Student's Introduction to English Grammar.
Hatcher, Anna Granville, 1949. "To get/be invited". Modern Language Notes.
Alexiadou, Artemis. "A note on non-canonical passives: The case of the get-passive." (http://ifla.uni-stuttgart.de/institut/mitarbeiter/alexiadou/files/noncanonical.pdf)
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