In short

The passive puts the affected person first and demotes the doer to に: 先生が私をほめました -> 私は先生にほめられました Watashi wa sensei ni homeraremashita (“I was praised by the teacher”). Japanese goes much further than English: it can build a passive from a verb that has no object at all, to say that something happened to your disadvantage - 雨に降られました Ame ni furaremashita, literally “I was rained on”.

The rule

Step 1 - Build the form from the ない-form. Take the plain negative, drop ない, and add れる (Group I) or られる (Group II).

• Group I (五段): 書かない -> 書か + れる = 書かれる kakareru; 読まない -> 読まれる yomareru; 言わない -> 言われる iwareru (う-verbs go through わ, never ×言あれる).
• Group II (一段): drop る, add られる. 食べる -> 食べられる taberareru, 見る -> 見られる mirareru.
• 来る -> 来られる korareru, with the ko- reading, exactly as in 来ない konai.
• する -> される sareru. This one breaks the trick (×しれる), so learn it as a fixed pair. Any noun + する follows it: 発表する -> 発表される, 注意する -> 注意される.

Step 2 - Every passive verb is a Group II verb. Once it ends in -れる／-られる it conjugates like 食べる, whatever it started as: 書かれます, 書かれません, 書かれました, 書かれない, 書かれた, 書かれて. You never need a second paradigm.

Step 3 - The direct passive: two particles move at once. The active pattern N1が N2を V becomes N2は N1に V-(ら)れる. The object is promoted to topic/subject, and the doer drops back to に.

• 先生が 私を ほめました。-> 私は 先生に ほめられました。

Write out that swap the first few dozen times you build a passive - を disappearing and に appearing is the whole grammar of the sentence.

Step 4 - Marking the agent: に, によって, から.

• に is the default, and covers almost everything: 母に注意されました。
• によって ni yotte is used with verbs of creating, producing or discovering, and generally in formal writing: この絵はピカソによって描かれました Kono e wa Pikaso ni yotte kakaremashita. The subject here is a thing whose origin is being described, and plain に would be unnatural.
• から can replace に with verbs of giving, telling or teaching, where the action visibly flows from a source (に stays correct too): 先生から注意されました, 母から言われました.

Step 5 - The possessor passive: the person is the subject, the thing keeps を. When someone acts on your belongings or your body, Japanese does not make the thing the subject. The owner becomes the topic, and the possessed noun stays marked with を:

私は弟にケーキを食べられました。 Watashi wa otōto ni kēki o taberaremashita.

Note that both に (the doer) and を (the thing) are present - a shape English has no equivalent of. The alternative 私のケーキは弟に食べられました is grammatical, but it sounds like a report about a cake; the natural Japanese reports what happened to you.

Step 6 - 迷惑の受身, the adversative passive. Here is the point where Japanese leaves English behind: the passive can be built from an intransitive verb - one with no object to promote at all - purely to say “this happened, and it affected me badly”.

• 雨が降りました。(“It rained.” - a neutral fact.) -> 雨に降られました。 (“I got rained on.” - and I was soaked.)
• 友達が来ました。(“A friend came.”) -> 友達に来られました。 (“A friend came on me.” - and my evening was ruined.)
• 子どもが泣きました。 -> 子どもに泣かれました。 (“My child cried on me.”)

The subject (usually 私) is normally left unsaid, the cause takes に, and the whole sentence carries a complaint. There is no way to translate this word for word - render the feeling: “I got caught in the rain”, “my child cried and I couldn’t cope”. This is the emblematic Japanese passive; if you understand 雨に降られました, you understand 受身.

Step 7 - The agentless passive: signs, notices and news. When the doer is unknown, obvious or irrelevant, leave them out entirely. This is the objective register of guidebooks, manuals and journalism: この店は1950年に建てられました, 会議は3時から行われます, and the very frequent hedge 〜と言われています to iwarete imasu (“it is said that…”). No に phrase appears at all.

Step 8 - Do not over-use it. English reaches for the passive to sound neutral or polite; Japanese does not. Where English says “the door was opened”, Japanese usually prefers the intransitive verb (ドアが開きました, see Transitive and intransitive verb pairs), and where English says “I was given a present”, Japanese uses もらいました (Giving and receiving). A passive with a human agent almost always implies you were affected, often unpleasantly - so a cheerful ×私は先生に日本語を教えられました reads as a grievance. Use the active unless something was really done to someone.

One form, three jobs. For Group II verbs and 来る, the passive is spelled exactly like the potential of lesson 37 - 食べられる is both “is eaten” and “can eat” - and it is also the light honorific of lesson 56. Particles settle it: an agent in に plus a surviving を means passive; an object marked が with no agent means potential. Spoken Japanese helps too, because ら抜き (食べれる, 見れる) applies only to the potential - so a full 食べられる in casual speech is usually passive. Group I verbs never clash at all: 読まれる (passive) vs 読める (potential).

Forms & patterns

Deriving the passive:

Conjugating a passive verb - always Group II:

Active -> passive: what moves where.

Choosing the agent particle:

Passive or potential? Read the particles.

Examples

Common mistakes

• 私は先生にほめました。 (Watashi wa sensei ni homemashita.) -> 私は先生にほめられました。 (Watashi wa sensei ni homeraremashita.) - に marks the doer, so the verb must carry the passive ending. As written the verb is still active, so the sentence tries to make you the one doing the praising.
• 私のケーキは弟に食べられました。 (Watashi no kēki wa otōto ni taberaremashita.) -> 私は弟にケーキを食べられました。 (Watashi wa otōto ni kēki o taberaremashita.) - the first sentence is not ungrammatical, but it reports on a cake; when the thing belongs to a person, Japanese makes the person the subject and the thing keeps を. Same for body parts: 私は足を踏まれました。
• 私は雨が降られました。 (Watashi wa ame ga furaremashita.) -> 私は雨に降られました。 (Watashi wa ame ni furaremashita.) - in the adversative passive the cause is the agent, and agents take に. が would make the rain the subject again and undo the passive.
• この小説は夏目漱石に書かれました。 (Kono shōsetsu wa Natsume Sōseki ni kakaremashita.) -> この小説は夏目漱石によって書かれました。 (Kono shōsetsu wa Natsume Sōseki ni yotte kakaremashita.) - verbs of creation take によって when the subject is the thing created; plain に belongs to sentences where a person is affected by an agent, so it clashes with a thing as the subject.
• 先生にほめれました。 (Sensei ni homeremashita.) -> 先生にほめられました。 (Sensei ni homeraremashita.) - ら抜き belongs only to the colloquial potential. A passive never loses its ら, in any register.

Tips

• The passive is an attitude, not a style. English uses it to sound neutral; Japanese uses it to say you were on the receiving end - usually unpleasantly. For neutral description choose the active or the intransitive verb (ドアが開きました), and for something nice done for you choose 〜てもらう／〜てくれる.
• “It rained on me” is the test sentence. If 雨に降られました and 友達に来られました feel natural to you, the adversative passive has landed. Both come from verbs with no object at all, which is impossible in English - so translate the complaint, never the words.
• に and を side by side in one clause is normal here. 私は弟にケーキを食べられました has the doer in に and the thing in を; 電車で足を踏まれました drops the doer entirely because nobody knows who it was. Missing を is the commonest error in this pattern.
• Group I gives you a free disambiguation. 読まれる vs 読める, 書かれる vs 書ける - only Group II and 来る are ambiguous with the potential, and in speech ら抜き usually resolves those too.