“tekkiri 〜to omotta”: I Was Sure / I Could've Sworn 〜 (a mistaken certainty) [JLPT N2]
By Nihongo to Japan · Updated July 3, 2026
“I was sure he would come, but…” — being convinced of something, only to find the conviction was wrong
“tekkiri 〜to omotta”: I Was Sure / I Could've Sworn 〜 (a mistaken certainty)
「てっきり ＋ 〜と思った／思っていた」 means “I was sure 〜 (but it turned out not to be)” — the speaker was firmly convinced of something, only to find afterward they were wrong. E.g. 「てっきり晴れると思ったのに、雨が降った」 (I was sure it would clear up, but it rained), 「てっきり彼が来ると思っていた」 (I was sure he'd come — but he didn't). It always pairs with と思った/思っていた, carrying the surprise of “I never imagined it wasn't so.”
🧠 Core nuance: I was 100% certain, and turned out completely wrong
The core is assuming something as a given, only for it to turn out the opposite: てっきり means the speaker at the time didn't doubt at all, took it as certain (sure it'd clear up, sure they were Japanese, sure he was the culprit), but the fact was otherwise, bringing an “ah, I was wrong” surprise and realization. It always looks back on a “mistaken past certainty,” so it must pair with と思った/思っていた, often followed by のに・が to bring out the gap with reality.
📌 How to Connect
| Form | Pattern | Example |
|---|---|---|
| てっきり〜と思った | I was sure 〜 (but not) | てっきり晴れると思った |
| てっきり〜と思っていた | I'd been sure 〜 | てっきり来ると思っていた |
| (often with) 〜のに/〜が | bringing out the gap | 〜と思ったのに、違った |
💬 Example Sentences
- てっきり今日は晴れると思ったのに、急に雨が降ってきた。(I was sure it'd be clear today, but it suddenly rained.) — wrong guess
- 流暢な日本語だったので、てっきり日本人だと思った。(Their Japanese was fluent, so I was sure they were Japanese.) — misidentification
- てっきり君が犯人だと思っていたよ。(I was sure you were the culprit.) — past certainty
- 返事がないから、てっきり断られたと思っていた。(With no reply, I was sure I'd been turned down.) — misjudgment
- てっきりもう帰ったものとばかり思っていた。(I'd been sure you'd already gone home.) — taking it as given
🔄 Compare: てっきり vs どうやら vs かと思いきや vs とばかり思っていた
| Expression | Nuance | Example |
|---|---|---|
| てっきり〜と思った | “I was sure 〜 (but wrong)” | てっきり晴れると思った |
| どうやら | “it seems 〜” (inference, possibly right) | どうやら本当らしい |
| 〜かと思いきや | “I thought 〜 but actually 〜” (expectation foiled) | 簡単かと思いきや難しい |
| 〜とばかり思っていた | “I'd been sure 〜” (synonym, emphatic) | 来るとばかり思っていた |
⚠️ Common Mistakes
- Not pairing with と思った: てっきり must pair with 「と思った/思っていた」; ✗ てっきり行きます (alone).
- For a correct inference: it's “I thought yet was wrong,” not for cases later confirmed correct.
- Feel: it carries the surprise of “utterly certain yet wrong,” not a plain inference.
- Position: てっきり sits at the head, modifying the following と思った.
💡 Nuance & When to Use
てっきり〜と思った means “I was sure 〜, but it turned out not to be,” where the speaker was firmly convinced of something (sure it'd clear up, sure they were Japanese, sure he was the culprit), only to find afterward they were wrong, with an “ah, I see I was wrong” surprise. It always looks back on a mistaken past certainty, must pair with と思った/思っていた, and is often followed by のに・が to bring out the gap. Distinguish from the inferential どうやら. Common in conversation. A must at N2.
🎯 JLPT Exam Tips
- High-frequency N2: てっきり〜と思った/思っていた = I was sure 〜 (a mistaken certainty).
- Must pair with: と思った/思っていた (can't stand alone).
- Distinction: てっきり (certain yet wrong) vs どうやら (inference, possibly right).
🖊️ 練習題（5題）
Q1. 「___晴れると思ったのに、雨が降った。」（還以為會晴）
(A) てっきり (B) どうやら (C) いよいよ (D) せっかく
Q2. 「てっきり」と必ず一緒に使うのは?
(A) と思った／思っていた (B) てください (C) なさい (D) だろうか
Q3. 「てっきり日本人だと思った」の含意は?
(A) 還以為是日本人（其實不是）
(B) 確定是日本人
(C) 不知道是不是
(D) 想成為日本人
Q4. 「てっきり」の語感は?
(A) 一口咬定地以為，結果錯了（意外）
(B) 客觀的事實
(C) 禮貌請求
(D) 強烈命令
Q5. 用法が自然なのは?
(A) てっきり君が犯人だと思っていた。 (B) てっきり行きます。
(C) てっきりを食べる。 (D) てっきりだ高い。
答案解析
1. (A) てっきり ── 還以為會晴(結果下雨)。
2. (A) ── 必配と思った/思っていた。
3. (A) ── 還以為是日本人(其實不是)。
4. (A) ── 一口咬定地以為,結果錯了。
5. (A) ── 「てっきり〜と思っていた」正確。