expressionspassive-voicesentence-construction
I found native people prefer to use passive voice in a sentence.
For example:
Tonight's moon can be seen from anywhere worldwide.
We have reason to believe that progress can be made.
Be honest, it's difficult for an English learner to understand.
Why not phrase it this way:
We can see the moon from anywhere worldwide.
In which cases do people prefer to use passive voice rather than active voice?
Here's what happened.
Once upon a time, people throughout the English-speaking world used the active voice and the passive voice according to whichever seemed to suit what they were trying to say. No one attached moral opprobrium to either, the people were happy, and there was peace throughout the land.*
Some human pursuits, such as administration and science, needed to make heavy use of the passive voice, because these pursuits are largely concerned with rules and results that are independent of the person who carried them out. Any competent member of the civil service should produce the same results given the same rules as any other. "The claimant's petition for a hunting license is denied, pursuant to §12345.67(g) of the Hunting Code." The result of a scientific experiment should depend on what was done, not who did it. "0.5 gm tin was heated to 15,000,000 ºC." Mentioning the name of the lab assistant who heated it would distract from the important facts, so the passive voice is appropriate. Similarly for bank tellers, accountants, optometrists, engineers, etc.
The language used by people in these pursuits was, and still is, precise, formal, and objective—"objective" in the sense that the person who "did" the action is irrelevant. The relationship between writer and reader is impersonal. You don't negotiate with administrators or scientists, finding a compromise between your and their unique desires and situations. They merely report results. And these people get a lot of prestige and respect.
It gradually dawned on people that if they wanted to sound formal and objective—and to get some of the respect given to professionals—they could use the passive voice even when it doesn't make sense or help communicate a thought. "It is imperative that steps are delineated for the establishing of time frames for socioeconomic priorities by responsible authorities." Similarly for highly abstract language, heavy use of the verb "to be", "big words" that derive from Latin, and other usage that's often needed legitimately in technical professions. When applied to most ordinary writing, such stylistic choices make the writing weak and unclear. "With regard to my summer vacation, the locations visited were felt to be memorable for a lifespan." I made up these last two examples as absurd parodies, but people were indeed imitating the sound of formal writing rather than using its conventions to communicate clearly.
By around 1910, many English teachers had noticed that students were resorting to pretentious, dull phrasing in their writing in an attempt to sound educated or formal. So they started advising their students to cut it out. Some produced pamphlets containing advice on how to write more clearly and forcefully. Today, the most famous of these is Strunk & White, a little handbook of advice to counter various bad stylistic choices that were common among college students in the early 20th century.
Now here's where our story starts to turn weird. Many schoolteachers are themselves the kind of people who maintain the stability of their society by upholding strict rules. They try to measure the performance of their students fairly and in conformity with the professional standards of their time, not according to their own "subjective" judgement. This has led schoolteachers many times to reduce good advice that requires thoughtful case-by-case judgement to foolish strict rules. Strict rules, foolish or not, are much easier to teach, enforce, and measure conformity to than good judgement. Good judgement is something you gradually cultivate, and it emerges in a unique form in each individual. No standardized test can measure that.
Once it had emerged among the most respected English teachers that the passive voice was often abused, rank-and-file schoolteachers began to "teach" that the passive voice was not just easy to abuse, but wrong. It's not just unclear, it's an attempt to dodge moral responsibility! Indeed the passive has always been the voice of choice for weasels, responsibility-dodgers, and obscurantists. George W. Bush famously said "He heard a bird flush, and he turned and pulled the trigger and saw his friend get wounded." That's Bush's way of saying "Dick Cheney shot his friend Harry Whittington with a rifle in a hunting accident" but taking care that you don't understand it. There's no limit to the number of examples of this kind of weaselly use of the passive voice that you can find to prove that the passive is evil. Of course, you can find just as many dishonest uses of every other grammatical form, too. People use the active voice to outright lie, but only the passive voice is the target of a moral crusade.
And so, every passive construction in an essay written by a student would be marked "passive" in red ink, with points taken off. Excuse me, I mean the schoolteachers would mark every passive construction that the student wrote and take points off. Whew, I almost sank into moral depravity for a moment there. Even when passive constructions specified the agent, as in "Harry Whittington was shot by Dick Cheney", teachers would mark it in red and penalize it. Many innocent constructions that merely look similar to the passive but aren't, like "The truck is now loaded," also got marked in red and penalized. It was like the Salem witch trials of 1692, only with a lot more red ink spilled.
Upon graduating high school or college, students were trained to spot anything that looked passive-ish and excise it. Or exorcise it. When desktop computers became commonplace, even grammar-checking software joined in the anti-passive frenzy—automatically marking every passive-ish-looking verb with a red underline and telling the user to change it to active voice. Computers, of course, are the ultimate in following rules without regard to common sense.
And that, dear Chen Li Yong, is why some English speakers (think they) don't like the passive voice. But we're not all like that. Actually, most people don't care. Most people still choose the passive or active according to whichever seems to suit what they're trying to say, without even thinking about it. Many teachers try to cultivate good judgement in their students, and many people do their best to exercise good judgement in writing, choosing the active or passive voice not by any simple rule but according to what's relevant, what they want to emphasize, what's clear, and what sounds good. Even anti-passive activists use the passive voice all the time (without noticing). It comes up in classes and writing guides more than in real life. The only real trouble is that when many people talk about how to revise a sentence, the mythology they were taught makes it hard to converse about it intelligently.
But wait, the story's not over. Many people have noticed that all this fuss over the passive voice is absurd. A new anti-anti-passive activism is on the rise among academics. Even now, they're crafting a new mythology: about how the passive voice became anathema. They're blaming Strunk & White for making a rule against it, which Strunk & White never did. New prescriptions are justified with "science" and Google Ngrams rather than custom, precedent, taste, and reasonable opinion. Even now, new forms of faux objectivity are taking root. Instead of resorting to the passive voice, students who want to sound "objective" today report facts by explicitly stating their source even when the source is irrelevant. In another ten years, probably another substitute for choosing words thoughtfully will arise, and reasonable people will ignore that, too.
So how does this affect you, a non-native speaker learning English?
Well, now you know that some of what you are taught about English is nonsense. Now you know that respected authorities contradict each other.
My advice is to ignore the advice to eschew the passive, and remember that the anti-passive activists are the crazy ones, not you. The passive voice is nearly always used innocently. It has many common uses, and is actually indispensible in English. Crusading against the passive voice because it can be abused makes as much sense as crusading against the present tense or the third person; those can be and are abused, too.
But you could reasonably disagree with my advice. As you gain mastery of English, you should gradually become more confident in choosing how you want to use the language. You should explore different forms of expression, read a variety of authors, see how flexible the grammar really is, and develop your own style through experience—just as every native speaker does.
*Actually, England was at war almost continuously during this time. This is a fable. Historical facts have been adjusted where necessary to support the moral. There never was a Golden Age, not even in regard to English grammar.
There is no absolute rule that governs when you should use the it version and when not. In my opinion (I speak American English), the it version is the more conversational of the two:
They say he doesn't like children. colloquial
People say he doesn't like children. conversational
It's said he doesn't like children. slightly circumspect conversational
He is said to dislike children. educated register conversational verging on stilted
Again, to my American English ear:
We understand he lives abroad. neutral
It is understood he lives abroad. formal
He is understood to live abroad. stilted
Best Answer
The passive voice exists for a reason; as far as I can tell all languages have some way of creating a construction equivalent in semantics (and pragmatics) to the English passive.
At the semantic level, the passive voice operates on transitive verbs (=2 or more arguments; note that the subject is included as an argument) and "promotes" the transitive object to a subject. The meaning is equivalent semantically (barring idiomatic usages), as the subject of a passive construction is still the object of that transitive verb. Consider these two sentences below, where the event (=what happens to the object) is the same, in either active or passive voice.
1) John ate [the cake]
2) [The cake] was eaten (by John).
In either 1) or 2), this information is the same: there was a salient cake and it was eaten. However, note that the passive allows one to drop out the agent.
So, why would one use the passive voice over the active? Perhaps the writer/speaker wants to give attention to the object. In English the subject position is often where topics go, and so is considered the "important" element. Promoting the object to a subject via passive allows one to emphasize this. Another possible case: we simply don't know who the agent was or perhaps the agent doesn't really matter. The passive is also helpful for generalizing / avoiding assigning blame / being polite.
Consider these cases:
3) The trash can was blown over (by the wind).
4) John was really screwed.
5) That project got really messed up. (<= note how it doesn't blame anyone in particular)
In 3), it probably obvious what blew the trash can over (in general people don't go around blowing down trash cans, etc.). For 4), this begins to get idiomatic--we could try to attribute reason(s) why John is not in a good situation, but usually this is secondary to stressing that John is really screwed.
We can apply this reasoning to the example sentence you gave:
6) [Tonight's moon] can be seen from anywhere worldwide.
In this sentence, the fact that the moon is visible from anywhere in the world is being stressed, hence why the writer probably chose to use the passive. We really don't care who is seeing the moon.
You should use the passive when its the idiomatic way to talk about an event (e.g. the agent usually is implied or not important) or when you want to focus on the object of such an event, and therefore promote it to subject position via the passive construction.