Choose the passive when the thing done is what the sentence is about and the person who did it is unknown, obvious, or beside the point. It is a decision about which noun goes into the first slot, and it is not a decision about style.
English puts what the reader already knows at the front of a sentence and the new part at the back. The subject slot is therefore the joint between one sentence and the one before it, and the passive exists so that you can keep a topic in that slot even when it is not the thing doing anything.
Eight sentences that show when it earns its place
- The window was broken. Be plus the past participle, and the doer has left the sentence entirely.
- My bike was stolen last night. The passive is right because the doer is unknown, which is the commonest legitimate reason to use it.
- the doer takes by. The report was written by Amara, and if the by phrase adds nothing, leaving it out is the whole point.
- He was given a medal. English can make either object the subject, so a medal was given to him also works, which most languages cannot do.
- The bridge is being repaired. The continuous passive, needed whenever the action is in progress, and the form learners most often avoid.
- She got fired. Get replaces be in informal speech and carries a sense that the subject was affected rather than merely acted on.
- I was born in Lagos. Born exists only as a passive, and I born is a fossilised error that survives for years.
- It is said that, which distances the writer from the claim. This is the passive hiding a source, and recognising it is a reading skill.
The first slot is a joint, not a promotion
Look at what happens across two sentences. The bridge opened in 1890. It was designed by a Scottish engineer nobody has heard of. The second sentence is passive because the paragraph is about the bridge, so the bridge has to stay at the front, and the engineer is the news and belongs at the back. Write the same pair of facts in a paragraph about the engineer and the active version is the right one, with no change in the facts at all.
That is why the advice to prefer the active is only half a rule. It is sound whenever the doer is the thing under discussion, and it is wrong whenever the doer is a detail, which in a report or a set of instructions is most of the time.
The doer is not moved, it is deleted
An active sentence carries the doer whether you want it or not. A passive one carries it only if you add by, and most passives do not: the samples were frozen overnight names nobody, and no reader can recover who froze them. That deletion is the only thing on this page that removes information rather than rearranging it, and it is the reason the passive gets a bad reputation it half deserves.
Used honestly the deletion is a courtesy, because nobody wants to read a technician whose name is not recorded froze the samples. Used dishonestly it is the whole point, and English has a famous specimen: mistakes were made, a complete sentence containing an admission and no admitter.
Where it stops: the reporting passive
Learners can convert an active sentence into a passive one in an exercise long before they ever choose a passive while writing, and the gap between those two abilities does not close on its own. It shows up first in academic and report writing, where a specific family of passives does work nothing else does: it is thought that, the results are shown in the table, he is said to have left.
Those are exactly the ones a conversion drill cannot teach. There is no active sentence behind it is thought that to convert from, because the doer was never a particular person, and a learner who has only ever transformed sentences has no route into the form at all. They write many people think that instead, which is a claim about many people and a much weaker sentence than the one they wanted.
Where the frames are collected
The Academic Phrasebank, kept by the University of Manchester and free to read without an account, lists these frames sorted by the job they do rather than by their grammar. It replaced copying sentence patterns out of published papers by hand, which is what everybody did before it and which took a term to build badly.
Its limit is the one that matters in a marked piece of work. It hands you a frame for reporting a claim; it cannot tell you whether the claim you drop into the frame is yours or somebody else's, and that distinction is what a marker is reading for. A frame borrowed to hide the difference is worse than a plain active sentence that owns it.
What it looks like when it goes wrong
Two failures, and they pull in opposite directions. The first is the passive reached for because it sounds formal, which produces it is believed by many people that, a sentence that has both named the doer and demoted it and gained nothing for the extra four words. The second is stripping every passive out of a report, which forces you to invent a subject for each one, and the invented subjects are almost always vaguer than the deletion was.
Which slot a noun can occupy in the first place is set by where English insists, and where it lets you choose, and the reporting frames above overlap with moving what someone said back one step in time, both inside the rules that decide what a sentence is allowed to mean.
The question left over is bigger than the passive and it is the one worth taking next: if the first slot is where a sentence joins the one before it, then the thread running through a paragraph is being carried by which nouns you put first, and that is a decision made at the level of the paragraph rather than the sentence. It belongs to emails, essays and reports that read like a native wrote them.