Let's begin with what I'm going to call 'short passives with be'. These are sentences like
"President Kennedy was assassinated". Notice that the verb assassinate in its ordinary
active usage has the assassin as the subject and it has the unfortunate person who ends
up dead as the direct object. That's what you find in an active clause like "Oswald
assassinated Kennedy." The hallmark of the passive is that the verb appears in the past-participle
form, and things are reversed, intuitively, so that a noun phrase that would have been
in the verb phrase now is the subject and, in the case of a be passive, there's an additional
verb, a verb be in its past-tense form "was": "Kennedy was assassinated". That is a simple
short passive with be.
A short passive doesn't have an exact counterpart in active form because clauses in English,
if they have tense, need a subject. And in the active, the person, in this case the assassin,
would have to be the subject. You can't just leave it out. So "Kennedy was assassinated"
doesn't have a direct active correspondent. You would only have "Assassinated Kennedy"
and nobody to fill the subject role.
So it's the long passives, like "Kennedy was assassinated by Oswald." that do have active
counterparts. "Oswald assassinated Kennedy" is the active counterpart of the long passive
"Kennedy was assassinated by Oswald."
Now, that's a very simple case. There are other kinds of passive as well. One that might
as well be mentioned as early as this, though it's very often overlooked (I don't know any
traditional grammars that even mention it), is the prepositional passive. A short prepositional
passive is something like "He was laughed at." A long prepositional passive would have
a by-phrase in addition: "He was laughed at by his contemporaries." In these cases, you
don't have a direct object; you have the object of a preposition, the preposition "at" in
this case. And it's the object of the preposition "at" in an active clause like his contemporaries
laughed at him. That is the subject in the passive. "He was laughed at by his contemporaries"
has this unnamed person "he" as the subject. And notice that 'he' is not the guy who is
laughing -- it's the contemporaries who are laughing. So things have been switched around,
but it's not just subjects and objects. In this case, it's subjects and objects of prepositions.
That is an additional kind of passive.
Now, I've been using examples, as all the introductory books do, that involve the word
'be', but contrary to what they say, it isn't true that passives always contain 'be'. You
can have passive clauses with no auxiliary verb at all. I'll give you a couple of examples.
They can't of course be full tensed clauses, because in a passive the crucial verb that
carries most of the meaning has to be in the participial form, and participles are not
tensed, so they can't be the main verb of a tensed clause. But you do find passive clauses
without 'be' used as adjuncts in cases like "That said, Korea is not the Philippines."
'That said' is the crucial bit. It has a subject ('that') and a past-participial verb ('said'),
and it makes a whole bare passive clause. I'm going to call them bare passives because
they're kind of naked without their auxiliary and they can't be put into a tensed form without
being clothed in an auxiliary that can accept the tense. You'd have to have an 'is' to get
something like "That is said". But you can use "That said" with the meaning "Given that
we've said that" as an adjunct at the beginning of a main clause.
The other context in which you will find bare passives is newspaper headlines. An example
like "28 injured in accidental detonation". That was in the Los Angeles Times back in
2013 as a headline. Headlines don't always need the auxiliary verb, the tense and so
on. They sometimes also lack other obligatory items like articles. It means, in effect,
28 people were injured in an accidental detonation or 28 people have been injured... it doesn't
make that clear. But it's clear enough for a headline. It catches the main content of
what's going on. That's another example of a bare passive clause.
Passive clauses also occur embedded in active clauses with certain verbs. There are transitive
verbs to do with causing or beginning or perceiving that take passive clauses as their second
complements. So you have sentences like "The government had the case investigated by the
police". It has the same meaning as "The government had the police investigate the case". But
that latter part, "investigated by the police", is a passive clause. And it occurs along with
a noun phrase that is the direct object for the main clause verb ('have') to make a sentence
that involves subject, a transitive verb, a direct object for the transitive verb, and
a passive clause. It's not just the verb 'have'. You also get verbs like 'see' and 'hear':
"I saw him knocked down by the taxi" is another example of the same type. And 'get' is one
of the transitive verbs that can do this: "She went out and got herself arrested". Which
entails, incidentally, that what she did was to obtain for herself the state of having
been arrested. It's not as if it just happened to her; she deliberately took some action
to get arrested. That's one of the special properties of the use of the verb 'get' like
that.
The term 'adjectival passive' is often applied to cases like "The door was locked" in one
of its meanings. It has two meanings, because if I say "The door was locked at exactly 6:00
by the security man", we're describing an action that the security man took. But you
can say "When we got there, we found that the door was locked", meaning simply that
it was in a locked state. And that's rather like saying "We found that
the door was impenetrable". It's very much like an adjective, but it looks like the past
participle of a verb, so it's often called an adjectival passive. So there's one more
type of passive that we have to take account of.
Yet another kind of clause that is definitely within the class of passives is the kind with
'get'. I said that you don't have to have a 'be' in a passive. You can have the verb
'get' in its intransitive use instead: "He got arrested" is a passive. And here, I would
say it weakly implies that it might have been his fault, or perhaps it was just an unfortunate
thing for him that it happened, but it doesn't really entail that. It's less formal than
the passive would be. You might be less inclined to write it in serious prose. And because
the suggestion is that the subject had something to do with bringing this about, there are some
cases where you wouldn't really want to use it. So you might say "He got knocked off his
bike", meaning someone knocked him off his bike, and that's implicitly rather bad news
for him. But you wouldn't say "The ring got given to somebody else" because there's no
way a ring brings it upon itself that it gets given. That just sounds a very weird way to
talk.
So 'get' passives will be found mainly with subjects that denote human beings. Otherwise,
with their past-participial verbs following the 'get', they are very much like 'be' passives.
It's just that, again, the traditional books virtually never mention 'get' passives. There
are all these different kinds of passives, and virtually none of them are mentioned in
the standard sources, the books on grammar, the hundreds of books on grammar that have
been published over the last two hundred years.
I'll mention one other kind of passive. It's the least important, I suppose, but you can
find passives where it's not a past-participial verb, it's a gerund-participial verb, the
kind of verb that ends in -ing. You can say "This rug really needs washing". And when
you think about it, washing is done by human beings, not by rugs. So to say that the rug
washed something is incoherent: rugs don't do that. When you say "The rug needs washing"
you mean the rug needs to be washed. So there is a use of the gerund-participle, ending
in -ing, that can carry the passive meaning. That's a variety of passive clause as well.
So here we have six or seven or eight different kinds of passive clause, virtually none of
which are ever mentioned in the books except for the first two: the short 'be' passive,
and the long 'be' passive. And two contradictory charges are made about them, and they're often
switched back and forth. The short passives, which don't mention the identity of the extra
person who would have been the subject in the active, the passives like "Kennedy was
assassinated", are accused of being evasive because they don't tell you who did it. Now
of course, most often when something unexpected happens, you don't initially know who did
it anyway and sometimes it doesn't matter who did it. When you say "The patient was
diagnosed with a rare form of cancer". we're thinking about the patient and the diagnosis,
and there was some specialist who made the diagnosis but it might hardly matter for the
story at this point if we're concerned with the patient. There's no reason to specify
in every case who did it -- who exactly was the doctor who did the diagnosis?
Sometimes it doesn't matter. In the case of the Kennedy assassination in 1963, for many
hours, nobody knew who had done it. A shot rang out, Kennedy was assassinated, but that
was the way to report it, because Lee Harvey Oswald's complicity in the crime was not discovered
until much later. So it is silly to say that it's evasive to use a short passive at all.
It's also silly to say that it's wordy and verbose, which is another charge that's levelled
at it. Passives are not verbose and wordy: short passives are often actually shorter
than the active counterparts. There are fewer words in "President Kennedy has been
assassinated" than there are in "A man called Lee Harvey Oswald has assassinated President
Kennedy." So you can be shorter and more brief and concise and to the point with a passive
than you would have been.
If you want to specify the agent, you can add the by-phrase. But, in that case, you're
focusing very clearly the attention on the by-phrase because it comes as the last
thing in the verb phrase, or relatively late in the verb phrase. It's excellent for focussing
attention on who it was that did it. So you can't level both the charges at both kinds
of passives. The charge of being evasive by not saying who did it can only be levelled
at short passives, and the charge of being wordy could only be levelled if at all at
the long passives, which have two extra words, 'be' and 'by', that you could have got away
with not using, if you'd chosen an active instead. But two little words? Nobody cares
about two little monosyllables. It's not a very serious charge against passives.