Structure
Verb + とき
[い]Adjective + とき
[な]Adjective + な + とき
Noun + の + とき
Details
Standard
About とき
とき, or 時 in kanji, is a noun that is regularly used to signify 'when' something happened (a verb). However, unlike some other time expressions, とき is mainly used to express things that happen at regular intervals (habits, hobbies, etc.), or at broad times/individual events (when it rains, when there is a sale at the shop, etc.)
Using とき is quite easy! You just need to attach it to the end of any independent word (verbs, nouns, or adjectives). As with most cases where a noun will be attached to another word in Japanese, we will also be required to use な after な-Adjectives, and の after nouns. The case-marking particle に will generally come directly after 時, signifying that another verb is about to follow.
Caution
As discussed previously, ときに is primarily used to discuss when things happened. What this means is that it will not be used to highlight ongoing states that were true during the first action. For example 'the time you tripped over a log on Tuesday'.
When とき is used, the nuance will be that it is describing one thing leading to another, rather than a static thing.
Synonyms
Related
Examples
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散歩をするときに音楽を聴く。
I listen to music when I take a walk.
授業のときは静かにしなくてはいけない。
When you are having class, you have to be quiet.
あの映画を見たとき、泣いた。
When I watched that movie, I cried.
大変なときに彼の親は亡くなった。
His parents died when he was going through a difficult time.
寒いときは、お風呂に入りたくなる。
When it is cold, I want to take a bath.
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Self-Study Sentences
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"IF" / "WHEN" (と vs たら vs とき) Differences ┃PART1 & 2
Japanese Ammo
Use とき
JapaneseAmmo
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[AIAIJ] An Integrated Approach to Intermediate Japanese
Page 114
[DBJG] A Dictionary of Basic Japanese Grammar
Page 13 & 490
Genki II 1st Edition
Page 78
Genki II 2nd Edition
Page 104
Marugoto Elementary 1 (A2) Rikai
Page 34
Marugoto Elementary 2 (A2) Rikai
Page 58
みんなの日本語 I
Page 146 [CH 23]
みんなの日本語 II
Page 24 [CH 28]
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とき – Grammar Discussion
Most Recent Replies (10 in total)

jelly1
Exactly my thoughts. The introduction/first example says it can be used for individual events but the Caution box says the opposite. Completely contradictory.
Would be nice if we could get that point about に added to the page as well.

Lederhosen42
Here to add onto the folks who are confused by the fact that the first example sentence is seemingly completely contradictory to the information given in the Caution section. Spent a fair amount of time scouring the first example and Caution section examples to work out what the difference was, but couldn’t work out what it would be.

Dasutin
For those struggling with when to use に, first let’s use は
寒いときは、お風呂に入りたくなる。
Being cold serves as a condition for wanting to take a bath.
You’ll notice that in the other examples that use は, the expression beforeときは is setting the condition required for what follows.に just marks the expression as the time period when something happened. If it’s clearly marking the time period, it can be dropped in casual conversation which is what’s happening in the sentences that drop it. But sometimes dropping it can make the sentence hard to read or unclear especially if theres a lot going on in the preceding expression.
You also want to make sure to use に if two events are overlapping. Like, “When I was leaving my house, the phone rang.”