Learn Hardcore Chinese: Tā kànzhe kànzhe shū, jiù shuìzháo le. - As he was reading and reading, he fell asleep.

看着 (kànzhe) means “is/was reading”, focusing on an ongoing action or state.
看着看着书 is like saying “(He) was reading and reading the book…” or “while he was reading the book…”.

The reduplication 看着看着 has two effects:

It emphasizes that the action continues for a while: reading along, continuing to read.
It sets up a background action from which something else unexpectedly happens:
看着看着书，就…… → “while he was reading the book, (then) …”

So 看着看着书 = “as he read the book / while he kept reading the book”.

Why is the last 着 in 睡着了 pronounced zháo instead of zhe? Is it the same character?

Yes, it is the same written character 着, but it represents two different words:

zhe (neutral tone) – aspect particle
- Used in 看着看着书 (kànzhe kànzhe shū).
- Indicates an ongoing action/state: “is/was doing”.
zháo (second tone) – result complement
- Used in 睡着了 (shuìzháo le).
- Means “to succeed in doing, to get into a state”.
- 睡着 = “to fall asleep / to succeed in sleeping” (reach the state of sleep).

So:

看着 (kànzhe) → ongoing action: reading
睡着 (shuìzháo) → result state: has fallen asleep

What overall pattern is 看着看着……，就……? How does it work?

This is a very common pattern:

V 着 V 着，就 ……

Meaning: “While doing V (and continuing to do it), then … (something else happens, often unexpectedly or naturally).”

In this sentence:

看着看着书 → “while (he was) reading the book / as he kept reading”
就睡着了 → “(he) then fell asleep”

So the whole structure is:

Background continuing action: 看着看着书
Sudden / natural result: 就睡着了

Other common examples:

走着走着，就迷路了。
While walking, (he) got lost.
聊着聊着，就哭了。
While chatting, (she) ended up crying.

Could I just say 他看着书，就睡着了? Is there any difference?

Yes, 他看着书，就睡着了 is perfectly correct and natural.

Differences in nuance:

他看着书，就睡着了。
→ Simply “He fell asleep while reading a book.”
The action is ongoing; then he falls asleep.
他看着看着书，就睡着了。
→ Adds more of a process / gradual feel:
“As he was (kept) reading the book, he (eventually) fell asleep.”

So 看着看着 makes it sound more vivid and gradual, but it is not required for grammaticality.

What is the function of 就 (jiù) here? Can I leave it out?

In 就睡着了, 就 has several nuances:

Marks quick succession: one thing happens right after another.
Often carries a feeling of something happening rather easily / naturally / unexpectedly.

So:

看着看着书，就睡着了。
→ “While he was reading the book, he (then) fell asleep.”
(The sleep comes directly out of the reading.)

You can say:

他看着看着书，睡着了。

This is still correct. Leaving out 就 makes the sentence a bit more neutral; 就 adds a light sense of “and then / just like that” and makes the sequence of events clearer.

Why do we need 了 (le) at the end of 睡着了? What is it doing?

There are two parts here:

睡着 (shuìzháo) – result complement: “to fall asleep / to get to the state of sleep”
了 (le) – perfective / change-of-state marker at the sentence end

Together, 睡着了 emphasizes that:

The event has happened and the new state is in effect now.
It is not just an ability, but an actual completed event of falling asleep.

Compare:

他睡着了。 → He has fallen asleep (he is now asleep).
他要睡觉了。 → He is about to go to sleep (change of state into “going to sleep”).
他睡着。 → feels incomplete in normal speech; usually you want 了 here.

So 了 marks that the result (being asleep) has been reached.

What is the difference between 睡着了, 睡了, and 睡觉了?

They are related but not the same:

睡着了 (shuìzháo le)
- Focus: the moment of falling asleep / entering sleep
- Implies the person is now asleep.
- Closer to “fell asleep”.
睡了 (shuì le)
- More general “slept / has slept / went to sleep”, depending on context.
- May focus on the action of sleeping, not just the transition into sleep.
- Often used with time expressions:
  - 他睡了八个小时。 → He slept for eight hours.
睡觉了 (shuìjiào le)
- Usually means “(someone) has gone to bed / is going to sleep now.”
- Commonly used to announce or describe the action of going to sleep:
  - 我要睡觉了。 → I’m going to sleep now.

In this sentence, we want the idea “he (ended up) falling asleep”, so 睡着了 is the natural choice.

Why does 看着看着书 put 书 only once at the end? Shouldn’t each 看着 have an object?

In actual speech, Mandarin often shares one object for repeated verbs.

他看着看着书 is understood as:

他看着书，看着书，就睡着了。
He was reading the book, (kept) reading the book, and then fell asleep.

For fluency, the object 书 is only said once, at the end, but it is logically attached to each 看着.

This kind of reduction is very common in verb-reduplication patterns; the repeated verb refers back to the same object without needing to repeat it explicitly.

What is the difference between 看着书, 在看书, and just 看书?

看着书 (kànzhe shū)
- Uses the aspect particle 着 (zhe).
- Emphasizes an ongoing state: in the middle of reading, or with book in hand, reading.
- Common in patterns like V 着 V 着，就…….
在看书 (zài kàn shū) / 正在看书 (zhèngzài kàn shū)
- Use 在 / 正在 as progressive markers.
- Also mean “is/was reading a book”, but more like the English “be + -ing”.
- Focuses on the time frame: what someone is doing at that moment.
看书 (kàn shū)
- Plain verb phrase: “read / to read books”.
- No explicit aspect; context decides if it is habitual or now.

In your sentence, 看着看着书 is chosen because:

着 easily forms the pattern V 着 V 着，就……, expressing “while doing X, then Y happened”.
在看在看书，就…… or 正在看正在看书，就…… would be unnatural.

Can I use the same pattern with other verbs, not just 看?

Yes. The V 着 V 着，就…… pattern is very productive. A few common examples:

走着走着，就迷路了。
While walking, (he) got lost.
听着听着，就哭了。
While listening, (she) started crying.
写着写着，就不想写了。
While writing, (I) then didn’t want to write anymore.
学着学着，就喜欢上了。
While studying it, (I) came to like it.

So you can plug in many different verbs to express “while doing X, then Y happened (often unexpectedly or naturally).”

Is 看着看着 like “reading and reading” (repetition), or more like “while reading” (background action)?

It has both flavors, but the main function here is “while doing”:

It does suggest repetition / continuation: reading and reading, going on reading.
But grammatically, in this pattern V 着 V 着，就……, it really serves to mark the ongoing background action from which another event arises.

So you can mentally read it as:

“As he was (kept) reading the book, he fell asleep.”

The English “reading and reading” feels a bit childish or literal; “while reading” is usually the best translation of the pattern.

Could I say 他看书，就睡着了 instead? What would change?

他看书，就睡着了。 is grammatically fine and understandable:

Meaning: “He fell asleep when/after he read / was reading.”

Differences:

Without 着, 看书 is more neutral, not explicitly marked as an ongoing state.
With 看着 or 看着看着, you highlight that he was in the middle of reading, and from that ongoing activity he drifted into sleep.

Nuance comparison:

他看书，就睡着了。
→ Simple sequence: he read, then fell asleep.
他看着书，就睡着了。
→ He was (in the process of) reading, then fell asleep.
他看着看着书，就睡着了。
→ He was reading away / reading along, and gradually / naturally fell asleep.

The original sentence is the most vivid and process-focused of the three.