Learn Hardcore Japanese: ie wo derutoki, kasa wo wasurenaide kudasai. - When you leave the house, please don’t forget your umbrella.

In Japanese, certain motion verbs like 出る (“to exit”) allow を to mark the place you leave. Here, 家を出る literally means “to exit the house,” so を indicates the location that’s being passed through or left. It’s not acting as a direct-object marker for 出る, but as a route/starting‐point marker. (You can also say 家から出る, which uses から to mark the origin more explicitly, but 家を出る is very common.)

What does 出るとき mean, and how does the ～とき clause work?

The phrase 出るとき combines the dictionary form 出る with とき (“time/when”). The pattern 辞書形 + とき means “when (one) does ~.” Here, 家を出るとき means “when (you) leave the house.”
Tip:
• V-るとき describes the time at or just before the action happens.
• If you used V-たとき, it would mean “when after having done ~.”

Why is the verb in 忘れないでください in the negative form with ～ないで plus ください?

To make a polite negative request (“please don’t ~”) you use the pattern 動詞ない‐form + で + ください. Here, 忘れないでください literally means “please don’t forget.”
• 忘れないで alone is a casual “don’t forget.”
• Adding ください raises the politeness level, suitable for formal or everyday polite speech.

Is there a difference between ～ないでください and ～なくてください?

Yes. The correct polite negative imperative is 動詞ない‐form + で + ください (e.g. 忘れないでください).
The form 動詞なくて + ください is not used for requests. If you say なくてください, it will sound ungrammatical to native speakers.

Can I say 家から出るとき instead of 家を出るとき?

Absolutely. 家から出るとき (“when leaving from the house”) uses から to mark the starting point, which is more explicit. 家を出るとき uses を to mark the same place as the route/exit. Both are correct; 家を出る is just a bit more idiomatic in everyday speech.

Why is there a comma after 出るとき? Do commas in Japanese work the same as in English?

The comma (読点) after 出るとき separates the time clause from the main clause (傘を忘れないでください) and signals a slight pause. Japanese comma usage is more flexible than English; it often depends on rhythm, clarity, or emphasis rather than strict grammatical rules.

Why is 傘を marked with を in 傘を忘れないでください?

忘れる is a transitive verb meaning “to forget,” so it takes a direct object. Here, 傘を忘れる means “to forget an umbrella,” and in the negative request 傘を忘れないでください you still mark 傘 with を as the thing not to forget.