Learn Hardcore Chinese: Tā tūrán kū le, yīnwèi tài lèi le. - She suddenly cried because she was too tired.

哭了
- Here 了 comes right after the verb 哭 (to cry).
- It marks a completed event / change of state: she (suddenly) cried / started crying.
- This is often called aspect marker 了.
太累了
- Here 了 is at the end of the clause.
- It marks a new or current state and often adds an emotional / exclamatory feeling.
- In the pattern 太 + adjective + 了, it means “so / too [adj] (now)” and often implies complaint or explanation.
- This is often called sentence-final 了 (change of situation).

So:

哭了 = the crying happened / started.
太累了 = she is (now) too tired, to such a degree that it explains what happened.

They share the same form but have different positions and functions.

Does 她哭了 mean “she cried” or “she started crying”?

In practice, both translations are possible, but the focus is on the moment the crying begins.

With verbs of sudden change (like 哭 “cry”, 笑 “laugh”, 死 “die”), adding 了 often highlights the transition into that state.
So 她突然哭了 is very naturally understood as:
- “She suddenly started crying” or
- “She suddenly burst into tears.”

If you want to emphasize duration, you add more information:

她哭了一个小时。 – She cried for an hour.
她一听到消息就哭了。 – As soon as she heard the news, she started crying.

In this short sentence, think of 哭了 as “(suddenly) burst into tears / started crying” rather than carefully describing how long she cried.

What exactly does 太累了 express, and how is it different from 很累?

Both describe being tired, but the tone and degree are different:

很累 (hěn lèi)
- Literally: very tired
- Neutral, descriptive: “She is very tired.”
- No strong emotional coloring by itself.
太累了 (tài lèi le)
- Literally: too tired / so tired (now)
- 太 means “too / excessively”, but in spoken Chinese it often works like “so extremely”.
- With final 了, it becomes emotional and explanatory:
  - “She is just too tired (that’s why this happened).”
  - “She is so tired (now)!”

So in this sentence:

因为太累了 suggests she was so exhausted that crying was a natural reaction.
It feels stronger and more cause-like than just 因为很累.

Why is there no 是 before 太累了? Why not 她是太累了?

In Chinese, adjectives can function as verbs meaning “to be [adjective]”. You don’t normally need 是 before a simple predicative adjective.

她累。 = She is tired.
她很累。 = She is very tired.
她太累了。 = She is too/so tired (now).

So 因为太累了 literally is “because (she) too-tired-le”, which equals “because (she) is too tired (now)”.

There is a pattern 她是太累了, but it has a different nuance:

她是太累了。 = “It’s that she’s really too tired.”
- Often used to emphasize the reason, sometimes in explanation or defense:
  - “Don’t blame her; it’s just that she’s too tired.”

In this sentence, we just want a plain reason, so 没有是 (no 是) is more natural: 因为太累了.

Why is there no subject before 太累了? Shouldn’t it say 因为她太累了?

Chinese often omits the subject in the second clause if it is obviously the same as in the first clause.

First clause: 她突然哭了 – subject is 她 (she).
Second clause: 因为太累了 – it is naturally understood that she is the one who is too tired.

So:

她突然哭了，因为太累了。
= “She suddenly cried, because (she was) too tired.”

You can also say:

她突然哭了，因为她太累了。

This is also correct, but:

Repeating 她 makes the sentence a bit heavier.
Native speakers usually drop it when there is no ambiguity.

You would keep 她 if you need to contrast different subjects:

她突然哭了，因为他太凶了。
She suddenly cried because he was too fierce.

I learned 因为…所以…. Why is there no 所以 here?

The textbook pattern 因为…所以… is real, but in natural speech and writing:

You do not always use both.
Which one you use depends on word order.

Two common patterns:

Reason first, result second
- You can use both or just 因为:
  - 因为太累了，所以她突然哭了。
  - 因为太累了，她突然哭了。
Result first, reason second (like in your sentence)
- You only use 因为, not 所以:
  - 她突然哭了，因为太累了。 ✔
  - 她突然哭了，所以因为太累了。 ✘ (wrong / unnatural)

So here the structure is:

[Result]，因为[Reason].
Therefore we only have 因为.

Can I move the 因为 part to the beginning? How does that change the sentence?

Yes, you can move the reason to the front. All of these are grammatical, with slight differences in focus:

Original:
- 她突然哭了，因为太累了。
- Focuses first on the event (she suddenly cried), then gives the reason.
Reason first:
- 因为太累了，她突然哭了。
- Puts the reason in the spotlight:
  “Because she was too tired, she suddenly cried.”
Reason inside the main clause:
- 她因为太累了，突然哭了。
- Literally: “She, because she was too tired, suddenly cried.”
- Feels slightly more compact and keeps 她 and 太累了 closer, as in
  “She, because of being too tired, suddenly cried.”

All three sound natural. The meaning is the same, but the information focus shifts:

Start with 因为 if you want to foreground the cause.
Start with 她突然哭了 if you want to foreground the sudden action.

What is the role of 突然 here, and can it be placed somewhere else?

突然 (tūrán) is an adverb meaning “suddenly”. The usual position for adverbs like this is before the verb or verb phrase:

她突然哭了。 – She suddenly cried / suddenly started crying.

Other common patterns:

她突然就哭了。
- 就 adds a feeling of immediacy / “right then”:
  “She just suddenly cried.”
她哭得很突然。
- This is 哭 + 得 + complement:
  “She cried in a very sudden way / Her crying came very suddenly.”
- Here you describe how she cried.

What you normally cannot do:

✘ 她哭了突然。 – Wrong / unnatural word order.

So, keep 突然 before the verb (or verb phrase), or use the 哭得很突然 structure if you want to describe the manner of the crying instead of just saying that it happened suddenly.

How do we know this sentence is talking about the past, if Chinese doesn’t have verb tenses like English?

Chinese doesn’t change verbs for past / present / future, but it uses:

Aspect markers like 了, 过, 在/正在, and
Context (time words, narrative context)

In this sentence:

哭了 has 了 after the verb.
- This shows the event of crying is completed / has occurred.
- In most contexts, English speakers will naturally translate this as past:
  “She suddenly cried / burst into tears.”
太累了 with final 了 describes a current or resulting state at that reference time:
- She ended up being too tired (and that explains the crying).

So the grammar is really about aspect (completed event, resulting state), but when you put it into English, it comes out naturally as a past-tense narrative:

She suddenly cried, because she was too tired.

Is 因为太累了，她突然哭了。 and 她突然哭了，因为太累了。 exactly the same, or is there a nuance difference?

They mean the same thing overall, but the information focus is a bit different:

她突然哭了，因为太累了。
- Starts with the event.
- Feels like: “She suddenly cried – (the reason is) because she was too tired.”
- Common in spoken language and storytelling where you first say what happened.
因为太累了，她突然哭了。
- Starts with the reason.
- Feels like: “Because she was too tired, she suddenly cried.”
- Slightly more formal / written and cause-oriented.

In everyday usage, both are fine. Use:

Result, 因为 Reason when you are narrating something that happened.
因为 Reason，Result when you want to foreground the cause or answer a “why” question.

Could I write it as two sentences: 她突然哭了。因为太累了。? Is that acceptable?

You do sometimes see that in novels, dialogue, or very informal writing, for stylistic effect:

她突然哭了。因为太累了。
- Feels like someone speaking in short bursts:
  “She suddenly cried. Because she was too tired.”

However, in standard written Chinese and for learners, it’s better to keep it as one sentence:

她突然哭了，因为太累了。

Reason:

因为太累了 is grammatically a subordinate clause (“because …”), which normally wants to be attached to a main clause.
Splitting it off as its own sentence is more of a rhetorical / literary choice, not the neutral default.

So: it can be done for effect, but the one-sentence version is the correct, neutral form to learn and use.