“toki vs baai vs sai ni” — Three Ways to Say “When…” [JLPT N3]
Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026
“When in trouble,” “in case of an earthquake,” “upon entry” — the nuance of とき, 場合 and 際, with examples. (JLPT N3)
「とき」「場合」「際に」 — three ‘when/in case,' which to use?
「地震のとき」「地震の場合」「地震の際に」 — all “at the time of an earthquake,” so how do these three differ? 「とき」 is the most general (a point in time), 「場合」 leans toward a hypothetical situation (in case …), 「際（に）」 is more formal and ceremonious (on the occasion of …). This guide sorts out this N3 “when/in case” trio at once — attachment, feel, and examples all covered.
Core: とき (a general time)／場合 (a hypothetical case)／際に (a formal occasion)
All three mean “when/in the case of ～,” with different emphasis:
- とき = when ～ (most general, a point in time or a period): 子供のとき、よく遊んだ (as a child, I played a lot).
- 場合 = in the case/event of ～ (leans ‘a hypothetical situation, in case'): 火事の場合は、階段を使ってください (in case of fire, use the stairs).
- 際（に） = on the occasion of ～, when ～ (a more formal, ceremonious setting): ご利用の際は、身分証をご提示ください (when using it, please present ID).
Feel: “when/in the case of ～” — とき neutral and general; 場合 stresses the hypothetical, conditional “(should some situation arise)”; 際に leans written and formal, for weightier acts/occasions.
Attachment & emphasis compared
| Form | Emphasis | Register | Example |
|---|---|---|---|
| 〜とき | a general point/period of time | colloquial～general | 出かけるとき |
| 〜場合 | a hypothetical case, in the event of | general (common in rules) | 遅れる場合 |
| 〜際（に） | a formal, ceremonious occasion | written, formal | 契約の際 |
Examples in use
- 日本へ行ったとき、京都に寄った。(When I went to Japan, I stopped by Kyoto.) — とき (general)
- 予約を変更する場合は、前日までにご連絡ください。(In case you change your reservation, please contact us by the day before.) — 場合 (hypothetical)
- お降りの際は、足元にご注意ください。(When alighting, please watch your step.) — 際 (formal)
- 若いとき、もっと勉強すればよかった。(When I was young, I should have studied more.) — とき
- 万一の場合に備えて、保険に入る。(To prepare for the unlikely event, I take out insurance.) — 場合 (in case)
⚠️ Easy traps to avoid
① 「場合」 leans ‘a hypothetical case, in case,' 「とき」 leans ‘a general point in time.' For “(should some situation arise) when …,” use 場合 (with a conditional, hypothetical flavor): 遅れる場合は連絡して (in case you'll be late, contact me — supposing a situation); for “(the) time point (of doing something),” use とき (plain time): 家を出るとき、鍵をかけた (when leaving home, I locked up — a time point). Rules and conditions take 場合, plain time takes とき.
② 「際（に）」 is more formal and written; everyday use takes 「とき」. 「際」 leans ceremonious, formal, mostly for procedures, ceremonies, notices (お申し込みの際, ご搭乗の際); everyday “when” takes とき (出かけるとき, rarely 出かける際). With customers or in notices 際 sounds polite; in chat とき is natural.
③ Attachment: nouns add 「の」, verbs use the plain form. noun ＋ の ＋ とき/場合/際 (地震のとき, 緊急の場合, 来店の際); verbs attach in the plain form (食べるとき, 遅れる場合, 利用する際). Mind past/present tense: 日本へ行くとき (before/en route) vs 日本へ行ったとき (after arriving) — the tense changes what “when” refers to, so don't get it wrong.
🔄 Compare with similar forms: とき／場合／際に／に際して
| Form | Feel | Example |
|---|---|---|
| 〜とき | when ～ (a general time point, most versatile) | 子供のとき |
| 〜場合 | in the case of ～ (hypothetical, in case, conditional) | 火事の場合 |
| 〜際（に） | on the occasion of ～ (a formal, ceremonious setting) | 契約の際 |
| 〜に際して | at the occasion of ～ (more written, weighty, major events) | 開会に際して |
💡 Learning tip
「とき・場合・際に」 all mean “when/in the case of ～,” sorted by emphasis and register: ① とき = a general time point/period (most versatile, 子供のとき, 出かけるとき); ② 場合 = a hypothetical case, in case (with a conditional flavor, 遅れる場合は連絡して, 火事の場合); ③ 際（に） = a formal, ceremonious occasion (written, ご利用の際, 契約の際). Three points: ① hypothetical cases and rule-conditions take 「場合」, general time takes 「とき」; ② formal, ceremonious settings take 「際」, everyday takes 「とき」; ③ attachment — noun ＋ の, verb plain form, and mind the “行くとき (before/en route) vs 行ったとき (after)” tense difference. Grasp “とき versatile, 場合 hypothetical, 際 formal,” and this set is clear.
❓ Quick FAQ
Q: 「場合」 and 「とき」 both render as ‘when ～' — when should I use 「場合」?
When what you mean is ‘(should some) situation arise,' with a hypothetical, conditional flavor. 「とき」 = when ～ (plainly a point in time or period, a time that actually happens or happened): 朝起きたとき、頭が痛かった (when I woke up, my head hurt — an actual time point); 暇なとき、映画を見る (when I'm free, I watch movies). 「場合」 = in the case/event of ～ (a hypothetical, conditional ‘if some situation appears,' common in rules and responses): 地震の場合は、机の下に隠れてください (in case of an earthquake, hide under a desk — supposing “should an earthquake occur”); 都合が悪い場合は、変更できます (if it's inconvenient, you can change it — supposing a situation). Test: if you can rephrase it as “if …” and it still flows, it's usually 「場合」 (遅れる場合 = if you'll be late); if it just means “the time of doing something,” use 「とき」 (遅れたとき = at the time you were late). So rules, conditions, contingencies (〜の場合は…) take 「場合」; general time, actual experience take 「とき」. Sometimes both work, but 「場合」 is hypothetical-heavy, 「とき」 time-heavy.
Q: How does 「際（に）」 differ from 「とき」? Can I swap them freely?
By register and the formality of the setting. 「とき」 = when ～ (neutral, versatile, usable from casual speech to general writing): 出かけるとき、電気を消す (turn off the lights when leaving — everyday). 「際（に）」 = on the occasion of ～, when ～ (more formal, written, ceremonious, mostly for procedures, ceremonies, services, notices — ‘formal acts/settings'): お支払いの際、クレジットカードもご利用いただけます (when paying, credit cards are also accepted — formal service language); ご搭乗の際は、シートベルトをお締めください (when boarding, please fasten your seatbelt — a notice). So: everyday, casual “when” → 「とき」; formal, ceremonious “on the occasion of,” for customers or notices → 「際」. Using 際 for everyday trifles sounds overwrought (e.g., ご飯を食べる際 is a bit grand; normally 食べるとき); conversely, a formal notice with 「とき」 sounds insufficiently dignified. Judge: formal addressee, ceremonious setting (service, procedure, ceremony) → 際; everyday → とき. For even weightier, major occasions (assuming office, an opening) there's also 「に際して」 (就任に際して一言申し上げます = on assuming office, allow me a few words — very formal).
🖊️ Practice Questions (5)
Q1. 「困った___は、いつでも電話して。」 (colloquial: when you're in trouble)
(A) 場合 (B) とき (C) 際に (D) ところ
Q2. 「緊急___は、このボタンを押してください。」 (manual/rule: in an emergency)
(A) とき (B) 場合 (C) 際に (D) ころ
Q3. 「ご来店の___、スタッフにお申し付けください。」 (business term: upon your visit)
(A) とき (B) 場合 (C) 際に (D) ところ
Q4. 「子供の___、よく公園で遊んだ。」 (reminiscing: as a child)
(A) 場合 (B) 際に (C) とき (D) ところ
Q5. 「合格しない___、もう一度受験してください。」 (rule/condition: in the case of not passing)
(A) とき (B) 場合 (C) 際に (D) ころ
Answer Explanations
1. (B) とき ── in casual everyday conversation, "when you're in trouble" → とき is most natural. 際に is too formal, 場合 leans toward rule-explanation.
2. (B) 場合 ── 「緊急の場合は〜してください」 = a rule/instruction (how to handle an emergency) → 場合.
3. (C) 際に ── 「ご来店の際に」 = business honorifics, upon your visit → 際に (the most formal).
4. (C) とき ── 「子供のとき」 = reminiscing about a period, とき is the broadest and most natural.
5. (B) 場合 ── 「合格しない場合」 = a hypothetical condition explanation (in the case of not passing) → 場合. For rule-like conditions like this, use 場合.