The principle behind all three patterns

Mandarin word order is sensitive to information status. A noun that is definite (already known, identifiable, 'the book', 'my friend', 'that man') behaves like a normal topic and sits before the verb. A noun that is indefinite (new to the discourse, 'a book', 'some person', 'an accident') is being introduced for the first time, and Mandarin prefers to introduce it after the verb.

• Known thing, normal subject position: 那个人来了 (nà gè rén lái le) - that man came (you and I both know who).
• New thing, post-verbal position: 来了一个人 (lái le yí gè rén) - a man came (someone, no one in particular).

English uses 'there is / there came' or a bare indefinite subject and lets intonation carry the difference. Mandarin moves the noun instead. Once you internalise 'new information goes after the verb', the three patterns below stop looking like separate rules and start looking like one. This is the same topic-before-comment instinct that governs basic word order and the ba-construction; here it decides which side of the verb a noun lands on.

Pattern 1: 有 for bare existence

有 states that something exists, usually at a place. The frame is Place + 有 + Indefinite Thing. The place is the topic (known); the thing introduced is new, so it follows 有.

• 桌子上有书。 (zhuō zi shàng yǒu shū.) - There are books on the table.
• 房间里有两个人。 (fáng jiān lǐ yǒu liǎng gè rén.) - There are two people in the room.
• 这儿有一个问题。 (zhèr yǒu yí gè wèn tí.) - There is a problem here.
• 门口有很多人。 (mén kǒu yǒu hěn duō rén.) - There are a lot of people at the door.

The thing after 有 is always indefinite. You cannot say 桌子上有那本书 to mean 'that book is on the table' - a definite, known book uses 在 instead: 那本书在桌子上 (nà běn shū zài zhuō zi shàng). That split between 有 for existence and 在 for the location of a known thing is the heart of location and existence; this page picks up where that one leaves off, with the verbs that introduce new things in motion rather than at rest.

Pattern 2: presentative 来 / 去 with an indefinite subject

The motion verbs 来 (come) and 去 (go) can present a brand-new participant. When the thing arriving or leaving is indefinite, it goes after the verb, often with the perfective 了. The frame is (Place/Time) + Verb + 了 + Indefinite Noun.

• 来了一个人。 (lái le yí gè rén.) - A person came / Someone has come.
• 昨天走了两个学生。 (zuó tiān zǒu le liǎng gè xué shēng.) - Two students left yesterday.
• 家里来了客人。 (jiā lǐ lái le kè rén.) - Guests have come to the house.
• 前面开过来一辆车。 (qián miàn kāi guò lái yí liàng chē.) - A car came driving up ahead.

Contrast a definite subject, which goes back in front of the verb where English would also expect it:

• 我的朋友来了。 (wǒ de péng you lái le.) - My friend came / has arrived. (a specific, known friend)
• 那个客人走了。 (nà gè kè rén zǒu le.) - That guest left.

So 来了一个人 and 一个人来了 are not free variants. The first announces a newcomer ('someone turned up'). The second, with the indefinite noun forced into subject position, sounds as if 一个人 were already on the agenda, and to a native ear it is faintly off. When you are introducing someone for the first time, put them after the verb. The 了 here is the perfective aspect marker doing its normal job; see aspect markers for why it attaches to the verb and not the sentence end.

Pattern 3: appearance and occurrence verbs 出现 and 发生

A small set of verbs mean, in themselves, 'come into existence' or 'take place'. The two you need at GCSE Higher are 出现 (appear, show up, emerge) and 发生 (happen, occur, break out). Because their whole job is to introduce something new, the thing that appears or happens lands after the verb. The frame is (Place/Time) + 出现/发生 + 了 + New Noun.

• 天上出现了一道彩虹。 (tiān shàng chū xiàn le yí dào cǎi hóng.) - A rainbow appeared in the sky.
• 屏幕上出现了几个字。 (píng mù shàng chū xiàn le jǐ gè zì.) - A few characters appeared on the screen.
• 昨天发生了一件大事。 (zuó tiān fā shēng le yí jiàn dà shì.) - A big event happened yesterday.
• 路上发生了一场车祸。 (lù shàng fā shēng le yì chǎng chē huò.) - There was a car accident on the road.

Note the measure words doing real work here (一道彩虹, 一件大事, 一场车祸); these classifiers are what mark the noun as a freshly counted, indefinite item. If classifiers are still shaky, see classifiers.

发生 in particular almost never takes a definite subject in front of it. You do not say 那件事发生了 in the neutral 'that thing happened' sense as your default; when the event is already known you topicalise it differently (那件事是昨天发生的, using the 是...的 construction to focus the time). For the plain 'something happened' that a learner reaches for constantly, the event goes after 发生: 发生了一件事 (fā shēng le yí jiàn shì), something happened.

Why 有, 出现 and 发生 are not interchangeable

They all introduce something, so learners blur them. They divide the labour cleanly:

• 有 = static existence. The thing is simply there. 桌子上有书 (there are books on the table). No event, no change, no time of onset.
• 出现 = a thing becomes visible or comes into being. There is a moment of appearance. 出现了一个问题 (a problem showed up) implies it was not there before.
• 发生 = an event takes place. The subject is typically an occurrence, not an object - 事 (matter), 事故 (accident), 变化 (change), 战争 (war). 发生了变化 (a change occurred).

A quick diagnostic: if you could rephrase the English with 'there exists', use 有; with 'there appeared / there emerged', use 出现; with 'there occurred / there happened', use 发生. You would not say a rainbow 'exists in the sky' as news, nor that an accident 'is there' on the road, and Mandarin draws the same lines.

Minimal pairs side by side

Hold the verb still and swap a definite subject for an indefinite one, and watch the noun jump across the verb.

Same verb, same vocabulary down each pair; only the definiteness of the noun changes, and that alone decides which side of the verb it sits on.

Common errors

Error 1: fronting a brand-new indefinite noun

The reflex from English is to put the doer first no matter what. With a new, indefinite participant, that reflex produces sentences that are grammatically parseable but pragmatically wrong - they imply the listener already knew about the thing.

• ✗ 一个人来了 (for 'someone came / a person came') - WRONG as a neutral announcement. Put the newcomer after the verb: ✓ 来了一个人 (lái le yí gè rén) - someone came.
• ✗ 一件事发生了 (for 'something happened') - WRONG. The event is new, so: ✓ 发生了一件事 (fā shēng le yí jiàn shì) - something happened.
• ✗ 一道彩虹出现了 (for 'a rainbow appeared') - off as news. ✓ 天上出现了一道彩虹 (tiān shàng chū xiàn le yí dào cǎi hóng) - a rainbow appeared in the sky.

If the noun carries 一个 / 一件 / 一道 and you mean it as fresh information, it belongs after the verb.

Error 2: using 有 where an event verb is needed

有 states existence, not occurrence. Learners reach for it to mean 'happen', because 'there was an accident' feels like existence in English.

• ✗ 昨天有了一场车祸 - WRONG. An accident is an event, not a thing sitting somewhere. Use 发生: ✓ 昨天发生了一场车祸 (zuó tiān fā shēng le yì chǎng chē huò) - there was a car accident yesterday.
• ✓ 路上有一辆车 (lù shàng yǒu yí liàng chē) - there is a car on the road is fine, because here the car simply exists at a location. The moment you mean the car arrived or crashed, you need a motion or event verb, not 有.

The test: 有 for what is there, 发生 for what took place, 出现 for what came into view.

Error 3: putting a definite noun after the presentative verb

The mirror image of Error 1. Once a noun is definite and known, it must go back in front of the verb. You cannot present something that is already on the table.

• ✗ 来了我的朋友 - WRONG. A specific, known friend is not new information. ✓ 我的朋友来了 (wǒ de péng you lái le) - my friend has arrived.
• ✗ 出现了那个人 - WRONG for a known person. ✓ 那个人出现了 (nà gè rén chū xiàn le) - that man showed up.

Post-verbal slot = new and indefinite. Pre-verbal slot = known and definite. Match the slot to the information status and these never go wrong.

Error 4: leaving off the measure word on the new noun

Because the post-verbal noun is being counted into the discourse for the first time, it almost always carries a number-plus-classifier. Dropping it sounds bare and unfinished.

• ✗ 来了人 (in most contexts) - thin and odd. ✓ 来了一个人 (lái le yí gè rén) - a person came. (Bare 来了客人 'guests came' is fine because 客人 reads as a quantity already; a singular count noun wants its 一个.)
• ✗ 发生了事 - WRONG. ✓ 发生了一件事 (fā shēng le yí jiàn shì) - something happened.

What to drill

1. New goes after, known goes before. An indefinite noun ('a / some / an') being introduced sits after the verb; a definite noun ('the / that / my') sits before it. This one rule covers all three patterns.
2. Split 有 from 出现 from 发生. 有 for static existence (桌子上有书), 出现 for something coming into view (出现了一个问题), 发生 for an event taking place (发生了一件事).
3. Never front a brand-new indefinite noun. 来了一个人, not 一个人来了; 发生了一件事, not 一件事发生了.
4. Don't use 有 to mean 'happen'. An accident, a change, a war is an event - 发生, not 有.
5. Keep the measure word on the post-verbal noun. It is being counted in for the first time: 一个人, 一件事, 一道彩虹.

For the rest-state side of existence (在 for a known thing's location, position words like 上 and 里), see location and existence. For why 了 attaches to the verb in 来了 and 发生了, see aspect markers. For the broader topic-comment instinct that puts known things first, see word order.