ACTIVE: Mary is doing homework for Jim.
PASSIVE: Jim is being done homework by Mary.
"<person> is being done <object>," can be used for some <object>s, but
homework is not one of them. "John is being done a service by Mary,"
is good. It's not a question of which words CAN'T be used in this type
of construction, but rather which ones CAN. Off the top of my head I
can only think of a few: "a service", "a wrong", "a favor".
BETTER: Jim's homework is being done by Mary.
ACTIVE: Henry is saying clever words to Jim.
PASSIVE: Jim is being said clever words by Henry.
This type of construction is very similar to the previous one but with
"said" in place of "done". I don't think I've ever heard a sentence
like this (with "said"). I can't point to a specific rule that it
breaks, but it just sounds bad.
ACTIVE: Who is knocking at the door?
PASSIVE: Who is the door being knocked at by?
There is either one or two problems with this, depending on whom you
ask.
1. The classic rule is, "Don't end a sentence with a preposition."
That rule is becoming less and less important as time goes by. I'm not
too concerned about that rule, unless breaking it makes the resultinig
sentence sound awkward. If you wanted to make the 80 year old grammar
teachers happy, the first revision would be to put the preposition
("by") with its object: "By who is the door being knocked?"
2. "Who" is a subject pronoun. A preposition, such as "by", needs an
object pronoun. The second rewrite would yield, "By whom is the door
being knocked?" Another option would be, "The door is being knocked by
whom?"
(Your other passive questions have the same problem or two.)
Let me say this about active and passive voices. While passive
sentences are technically correct, many people (who have thought about
it) prefer the corresponding active sentence. In general, the
predicate (main verb) of a sentence should be the action that is
important to the writer, and the subject should be the noun that is
doing the action.
"The professor threw the switch." The main action going on here is
throwing. Who or what did the throwing? The professor did. That, we
assume, is what the author is trying to convey, so the active version
is correct.
When would the passive, "The switch was thrown by the professor," be
the "correct" version? We'd use the passive version when the fact that
the switch is being thrown is more important than who is throwing it.
The switch was thrown. There, that's the important piece of
information.
Perhaps, a better practice would be to find sentences that are already
in the passive voice and...
A) Determine if the author really should have used the active voice
B) Change from passive to active.
You'll do the passive-to-active transformation MUCH more often than the
reverse.
I hope this helps.
(This being helpful is hoped by me.)
Ryan
