Learn Hardcore Chinese: chūmén de shíhou jìde dàishàng màozi. - Remember to put on your hat when you go out.

Here 的 turns the verb phrase 出门 (to go out / leave the house) into a modifier for 时候 (time; when). So 出门的时候 literally means “the time of going out / when (you) go out.”

In standard Mandarin you need the 的 here. 出门时候 without 的 is not standard and sounds wrong in most contexts.

What is the difference between 出门的时候 and 出门时?

They mean almost the same thing: when going out.

出门的时候 is more common in spoken Mandarin and feels more neutral and natural in everyday speech.
出门时 is shorter and a bit more formal or written-style. You’ll see it more in instructions, written notices, or formal texts.

In casual daily speech, 出门的时候 is usually the better choice.

Why is there no 你 in the sentence? How do we know it means “Remember to wear a hat when you go out”?

Imperative sentences in Chinese often omit the subject when it’s clearly “you” from context.

So instead of saying:

你出门的时候记得戴上帽子。

it is completely natural to drop 你 and just say:

出门的时候记得戴上帽子。

Native speakers automatically understand this as addressing “you,” similar to English instructions like “Push to open” (without saying “You push to open”).

Can I change the word order and say 记得出门的时候戴上帽子 instead?

Yes, 记得出门的时候戴上帽子 is also correct and natural.

出门的时候记得戴上帽子。
– Literally: “When (you) go out, remember to put on a hat.” (Emphasis starts with the time.)
记得出门的时候戴上帽子。
– Literally: “Remember to put on a hat when (you) go out.” (Emphasis starts with the act of remembering.)

Both are fine in daily speech. The difference in nuance is tiny; use whichever word order feels more natural to you.

What is the difference between 记得 and 记住 here? Could I say 出门的时候记住戴上帽子?

Both 记得 and 记住 relate to remembering, but they’re used a bit differently:

记得 (jìde) = to remember, to not forget
- Often used for ongoing memory or a gentle reminder.
- Very natural in instructions: 记得带伞。 – “Remember to bring an umbrella.”
记住 (jìzhù) = to firmly remember; to memorize and not forget again
- Emphasizes locking it into memory.
- Often used when teaching or scolding: 这个要记住！ – “You must remember this!”

In this sentence, 记得 is more natural and sounds like a gentle reminder.
出门的时候记住戴上帽子 is grammatically possible, but it sounds a bit stronger, like “Make sure you really remember to wear a hat (and don’t forget again).”

What does 戴上 mean compared to just 戴? Why do we use 上 here?

戴 (dài) by itself means to wear (for hats, glasses, jewelry, accessories).
戴上 (dài‑shàng) adds 上, a resultative complement, which emphasizes the action of putting it on and the result being that it is now on your head.

So:

戴帽子 – to wear a hat (in general).
戴上帽子 – to put a hat on / to get the hat onto your head.

In a reminder like this, 戴上帽子 is very natural because you’re talking about the action at the moment of going out, not just the state of “wearing a hat” in general.

Why do we use 戴 with 帽子 and not 穿?

Chinese uses different verbs for “wear” depending on the item:

戴 (dài) – for accessories worn on the head or face, or small items:
- 帽子 (hat), 眼镜 (glasses), 手套 (gloves), 耳环 (earrings), 项链 (necklace)
穿 (chuān) – for clothes you put your body into:
- 衣服 (clothes), 裤子 (pants), 裙子 (skirt), 鞋 (shoes), 袜子 (socks)

So for a hat, 戴帽子 / 戴上帽子 is correct; 穿帽子 is wrong.

Could I say 出门的时候把帽子戴上 instead of 出门的时候记得戴上帽子?

出门的时候把帽子戴上。 is grammatically correct, but the meaning and tone are a bit different:

出门的时候记得戴上帽子。
– “Remember to put on a hat when you go out.” (a reminder)
出门的时候把帽子戴上。
– More like “When you go out, put your hat on.” (a direct instruction, slightly stronger, no “remember”)

Also, the original uses 记得, which explicitly focuses on “don’t forget.” The 把 sentence just tells you what to do, without the “remember” nuance.

Why is it 帽子 and not just 帽? What does the 子 do?

In modern Mandarin, many nouns take an extra 子 at the end, and that form becomes the normal everyday word:

帽子 – hat
桌子 – table
筷子 – chopsticks

The shorter form 帽 exists, but:

It’s usually seen in compounds (e.g. 安全帽 “safety helmet”, 草帽 “straw hat”).
On its own in daily speech, 帽子 is the standard and most natural word.

So 戴上帽子 is what native speakers say; 戴上帽 by itself feels incomplete or unnatural.

Is this sentence polite or casual? How would I make it more polite?

出门的时候记得戴上帽子。 is neutral and slightly casual. Tone-wise, it’s like saying “Remember to wear a hat when you go out” to a friend or family member.

To sound more polite/formal (e.g. in a notice), you could say:

出门时请戴好帽子。
出门时请戴上帽子。

Adding 请 (“please”) and sometimes 好 (as in 戴好, “wear it properly / have it on”) makes the instruction more courteous or official.

Can I omit 的时候 and just say 出门记得戴上帽子?

Yes, 出门记得戴上帽子。 isalso natural and commonly said.

出门的时候记得戴上帽子。
– Slightly more explicit: “At the time when you go out, remember to put on a hat.”
出门记得戴上帽子。
– Shorter, more colloquial: “When you go out, remember to put on a hat.”

The meaning is essentially the same; dropping 的时候 just makes it a bit more compact and conversational.

How would I say “Remember to wear a hat when you go out in winter” using this pattern?

You can add 冬天 (in winter) as a time word before 出门:

冬天出门的时候记得戴上帽子。
– “In winter, when you go out, remember to put on a hat.”

Or, a bit shorter:

冬天出门记得戴上帽子。

Time expressions in Chinese usually go from bigger to smaller, so 冬天 (season) comes before 出门 (the action).