Learn Hardcore Chinese: wǒ de shìyǒu yǒushíhou huì bǎ hùzhào fàng zài shū li, suǒyǐ zǒngshì zhǎo bú dào. - Sometimes my roommate puts the passport inside a book, so she can never find it.

With one-syllable pronouns (我, 你, 他, etc.) before a close human relationship / familiar person word (朋友, 同学, 室友, 妈, 爸), 的 can be dropped in casual speech:
- 我(的)室友, 我(的)朋友, 我(的)妈妈
With longer noun phrases or when you want to sound a bit more formal/clear, you keep 的.

So:

我室友有时候会… (colloquial, natural in speech)
我的室友有时候会… (standard, also totally fine in speech and writing)

The sentence you gave is the fully explicit, standard form.

What exactly does 有时候 mean, and where can it go in the sentence?

有时候 (yǒushíhou) means “sometimes”.

In this sentence:

我的室友有时候会把…
→ My roommate sometimes will…

Position:

It usually goes before the verb phrase:
- 我有时候去图书馆。 – I sometimes go to the library.
Here it’s before 会, which is part of the verb phrase, so it’s fine:
- 我室友有时候会把护照放在书里。

You could also move it to the very beginning:

有时候，我的室友会把护照放在书里… – Sometimes, my roommate will put the passport in books…

All are natural; the meaning doesn’t really change.

What is 会 doing here? Is it future tense, ability, or something else? Can I omit it?

会 (huì) has several uses; here it mainly marks a typical / habitual tendency:

我室友有时候会把护照放在书里
→ My roommate sometimes tends to / will put the passport in books.

It’s similar to English “will” when talking about habits:

He’ll sometimes leave his keys at work.

It’s not emphasizing future time specifically; it’s about what he tends to do.

Can you omit 会?

我室友有时候把护照放在书里 is also grammatical and understandable.
With 会, the sentence sounds more like a pattern/habit.
Without 会, it can sound a bit more like you’re just describing an occasional action without stressing that it’s his typical way.

In everyday speech, both versions are used; 会 just adds that “that’s how he (often) behaves” feeling.

Why is 把 used here? What does the 把 construction do?

把 introduces a special structure:

[Subject] + 把 + [object] + [verb + complement/location]

It’s used when:

The object is known/specific, and
You want to focus on what happens to that object.

Here:

我的室友有时候会把护照放在书里
Subject: 我的室友 (my roommate)
把-object: 护照 (passport)
Verb + result/place: 放在书里 (put in books)

Using 把 emphasizes the passport being placed into the books as a result.

A very similar sentence without 把 would be:

我室友有时候会在书里放护照。

Differences:

把-sentence: highlights 护照 and what is done to it.
Non-把 sentence: highlights 在书里放 (the action “put in book(s)”).

Both are correct; 把 is very natural here because we’re describing what ends up happening to the passport specifically.

Is 放在书里 one unit? Why do we need both 放 and 在?

放在书里 is a verb + location pattern:

放 = to put / to place
在 + 书里 = in (the) book(s)

Together, 放在书里 means “put (something) in the books”.

Structure:

放 + 在 + [place]
- 把书放在桌子上。 – Put the book on the table.
- 把手机放在包里。 – Put the phone in the bag.

放 alone just means “to put” without telling where.
在 + 书里 alone would mean “is in the book(s)”, describing location, not the action of putting.

So you need both to say “put (it) in (the) book(s)”.

Why is it 书里 and not something like 在书里面 or 在书中? Are these different?

All of these are possible, with small nuance / style differences:

在书里 – in the book(s); very common and neutral.
在书里面 – “inside the book(s)”; 里
- 面 together; slightly more explicit, colloquial.
在书中 – “in the book(s)”; more formal/literary, common in written style.

In your sentence:

把护照放在书里 is the most natural everyday way to say it.
放在书里面 is also fine and colloquial.
放在书中 would sound written/formal for this kind of everyday situation.

So 书里 is just the ordinary spoken choice.

Why is there no measure word like 一本书 here? Why just 书里?

Here 书 is used in a general / non-specific way:

放在书里 = put (it) in books / inside some book or books.

You don’t care about which book or how many books; you just mean “in books” as a place where things are hidden, like saying in English, “He puts his passport in books.”

If you wanted to be specific:

放在一本书里 – in one particular book
放在那本书里 – in that book

But the sentence is describing a habit in general, so 书里 without a measure word sounds natural and vague, matching the idea “in (some) book(s).”

Why is 所以 used without 因为? Do we need 因为…所以…?

Basic pattern:

因为 A，所以 B – Because A, therefore B.

But in real usage:

You can say just 因为 A (and leave 所以 implied), or
Just A，所以 B (and leave 因为 implied).

In your sentence:

我室友有时候会把护照放在书里，所以总是找不到。
The reason is the first clause (putting the passport in books).
所以 introduces the result (always can’t find it).

You could also say:

因为我室友有时候会把护照放在书里，所以总是找不到。

That’s also correct, just a bit more formal/explicit. In everyday speech, using only 所以 here is completely natural.

What does 总是 mean, and where does it go relative to 不 and 找?

总是 (zǒngshì) means “always”.

In 所以总是找不到:

总是 modifies the whole verb phrase 找不到:
- 总是 + 找不到 → always can’t find (it).

Placement:

Frequency adverbs like 总是, 常常, 有时候 usually go:
- Before the main verb
- After the subject (if there is one in that clause)

Examples:

他总是迟到。 – He is always late.
我总是找不到钥匙。 – I always can’t find my keys.

When you also have 不, they go in order:

Subject + 总是
- Verb
  - 不/得/到 etc.
    - 总是找不到 (always can’t-find)
      You wouldn’t say 找总是不到.

So 总是找不到 is the natural order.

What is 找不到 exactly? How is it different from just 找? Why not 找不着 or 没找到?

找不到 is 找 (to look for) + the result complement 不到 (“unable to reach/achieve”).

So 找不到 means:

“(try to) look for (it) but can’t find it / fail to find it.”

Differences:

找 alone:
- 我在找护照。 – I’m looking for my passport. (no result implied)
找不到:
- 我总是找不到（护照）。 – I always can’t find (my passport).
  It implies you tried and failed.
找不着:
- Colloquial alternative, especially in northern speech:
- 我总是找不着护照。 – Same meaning as 找不到; slightly more conversational.
没找到:
- Past/result state: “didn’t find (it)”:
- 我找了半天，还是没找到护照。 – I looked for a long time and still didn’t find the passport.
- Focuses more on the final outcome of a specific attempt, not the general ability.

In your sentence, we’re describing a general, repeated situation (habit), so 总是找不到 is the natural choice: “always can’t find (it).”

Why is it 不 in 找不到, not 没? What’s the difference between 找不到 and 没找到 grammatically?

不 and 没 are different types of negation:

不: general, habitual, future, or “cannot” type negation; often used in potential/result complements.
没: past / factual non-happening or non-existence.

In 找不到:

不 is part of the result complement 不到: “unable to reach/find.”
Structure: Verb + 不到 / 得到 / 完 etc. shows can’t / can achieve a result.
- 看不到 – can’t see
- 听不到 – can’t hear
- 做不完 – can’t finish

You cannot use 没到 in that position to mean “can’t reach/find.”

没找到:

没 negates the verb phrase in a past/result sense:
- 没 + 找到 = did not find (on that occasion).

So:

找不到护照 – I’m unable to find the passport / I can’t find it.
没找到护照 – I didn’t find the passport (in that search / that time).

In a sentence about a habitual problem (“always can’t find it”), 找不到 with 不 is the correct choice.

Why is there no “it” after 找不到? Shouldn’t it be 找不到它 or 找不到护照?

Chinese often omits the object when it’s clear from context.

Earlier in the sentence we already mentioned 护照 (passport):

把护照放在书里，所以总是找不到。

It’s obvious that 找不到 refers to the passport, so you don’t need to repeat it.

You could say:

…所以总是找不到护照。 – …so (he) always can’t find his passport.

That’s also correct, just a bit more explicit.
找不到 on its own, after mentioning 护照, is very natural and not incomplete.

Why is 不 pronounced bú instead of bù in 找不到?

This is a standard tone sandhi (tone change) rule.

不 (bù) becomes bú (2nd tone) when it is followed by a 4th tone syllable.

In 找不到 (zhǎo bú dào):

到 (dào) is 4th tone, so 不 changes from bù to bú.

Other examples:

不对 → bú duì
不是 → bú shì
不要 → bú yào

When 不 is followed by a non-4th-tone syllable, it usually stays bù:

不忙 (bù máng), 不来了 (bù lái le).

Is 室友 exactly the same as “roommate”? Are there other words like 同屋?

室友 (shìyǒu) is the standard, common word for “roommate” (someone who shares a room or living space with you).

同屋 (tóngwū) literally means “same room.” It can also mean roommate, but:

室友 is more common in modern Mandarin for “roommate.”
同屋 shows up, but sounds a bit less modern/common in many contexts.

So in this sentence, 室友 is the most natural everyday choice for “my roommate.”

Could the word order be changed, like 有时候我室友会…? Would that sound different?

Yes, you can change the word order slightly without changing the basic meaning.

Original:

我室友有时候会把护照放在书里…

Possible variant:

有时候我室友会把护照放在书里，所以总是找不到。

Both mean “Sometimes my roommate will put the passport in books, so he always can’t find it.”

Nuance:

我室友有时候会… – starts with “My roommate…”, then adds “sometimes”.
有时候我室友会… – starts with “Sometimes…”, highlighting the time/frequency a bit more.

Both are natural; the difference is very slight and mostly about what you put in the listener’s mind first.

Why is there no 了 in 会把护照放在书里 or 总是找不到? Doesn’t Chinese often use 了?

了 often marks:

A completed event (verb-了) or
A change of state (sentence-final 了).

Your sentence describes a habitual situation, not a single completed event:

“My roommate sometimes puts his passport in books, so he always can’t find it.”

For general habits or repeated behaviors, Chinese usually does not use 了:

我常常忘记带钥匙。 – I often forget my keys. (no 了)
他有时候会迟到。 – He sometimes is late. (no 了)

If you added 了, it would sound like talking about a specific completed action, not a general habit:

刚才他把护照放在书里了。 – Just now he put the passport in a book. (one event)

So in your sentence, no 了 is exactly right because you’re talking about a recurring habit/problem.