“tekkiri…to omotta” Meaning & Usage — “I Was Sure (but Wrong)…” [JLPT N2]

Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026

“I was sure he'd come, but…” — being convinced of something that turns out wrong, with examples. (JLPT N2)

「てっきり彼が来ると思ってたのに、来なかった」 — I was sure, but I'd got it wrong

Waiting for someone who never showed, 「てっきり彼が来ると思ってたのに、来なかった」 (I was sure he'd come, but he didn't) — 「てっきり〜と思った」 = I was sure that ～, I'd assumed ～, used to express “(I) firmly believed something was so, only to find later I'd got it wrong.” It almost always carries the unspoken “it turned out to be otherwise.” This guide covers its use, pairing with 「と思った／思っていた,」 and how to tell it from 「とばかり思っていた.」

Core: sure at first, but got it wrong

「てっきり ＋ (plain form) ＋ と思った／思っていた」 means “(I) firmly believed, was certain it was ～, but it wasn't (I got it wrong)”:

• てっきり彼が犯人だと思っていた (I was sure he was the culprit [but he wasn't]).
• てっきり今日は休みだと思っていた (I was sure today was a day off [but it's a workday]).
• てっきり日本人だと思ったが、実は台湾人だった (I assumed they were Japanese, but actually Taiwanese).

Feel: “I was sure ～ (but it turned out…)” — the core is “sure at first → later found I was wrong”: the adverb 「てっきり」 itself carries the strong certainty of “(I assumed it must be) ～,” but the whole sentence's unspoken sense is “(I was sure, yet) it wasn't, I got it wrong.” So it almost always pairs with a turn like 「のに・が,」 or adds the truth afterward (“actually…”).

Attachment rules

Example sentences

• てっきりあなたも来ると思っていました。(I was sure you'd come too [but you didn't].)
• てっきりもう終わったと思っていたが、まだ続いていた。(I was sure it had ended, but it was still going.)
• 荷物が届かないので、てっきり忘れられたと思った。(The package didn't arrive, so I assumed I'd been forgotten [it was just delayed].)
• てっきり彼女は怒っていると思ったが、笑っていた。(I was sure she was angry, but she was smiling.)
• てっきりこれで合っていると思ったのに、間違いだった。(I was sure this was right, but it was wrong.)

⚠️ Where learners slip up

① It carries the unspoken ‘I got it wrong,' not a plain ‘assumed.' 「てっきり」's most important feel is “(I) firmly believed it was ～, only to find it wasn't, I got it wrong,” with the chagrin or surprise of “(oh,) so I was mistaken.” It's not a plain, neutral “assumed” — it foregrounds “I was dead sure, yet it turned out contrary to fact.” So 「てっきり〜と思った」 almost always implies a following “actually not”: てっきり男の子だと思っていたら、女の子だった (I assumed it was a boy, but it was a girl). It corresponds to “I was sure ～ (but it turned out…), I'd assumed ～, I was dead certain ～ (only to find).” Test: to express “(I was sure it was ～,) but I got it wrong” (with surprise/chagrin) → てっきり. (A plain neutral “I thought ～” just uses 「〜と思っていた,」 not necessarily てっきり.)

② 「てっきり」 is an adverb, always with 「と思った／思っていた.」 「てっきり」 is an adverb, can't stand as a predicate, and must pair with 「と思った／と思っていた／と信じていた」 (assumed ～, believed ～): ○ てっきり〜だと思った / × てっきりだった (× can't stand alone). It modifies 「思う (assume),」 stressing “(I) assumed with certainty that ～.” So seeing 「てっきり,」 「〜と思った／思っていた」 always follows. Mnemonic: てっきり ＋ (plain form) ＋ と思った／思っていた.

③ 「てっきり」 vs 「とばかり思っていた」: both ‘dead sure yet wrong,' close in feel. These two are close, both “(I) was dead sure / only assumed it was ～, but got it wrong.” 「てっきり〜と思っていた」: てっきり彼が来ると思っていた (I was sure he'd come). 「〜とばかり思っていた」: 彼が来るとばかり思っていた (I'd been assuming [only] that he'd come). Both carry “firmly believed, yet contrary to fact,” mostly interchangeable. Subtle difference: 「てっきり」 is an adverb (sentence-initial, stressing the “dead sure” certainty); 「とばかり」 attaches after the quoted content (〜とばかり思っていた, stressing “only thinking in that direction, not considering other possibilities”). In practice the two are often interchangeable: てっきり〜と思っていた ≒ 〜とばかり思っていた (both “I was sure ～, but it turned out…”). To express “I was dead sure at first, but got it wrong,” both are vivid.

🔄 Nuance & comparison: てっきり／とばかり思っていた／と思っていた／と思いきや

💡 Quick takeaway

「てっきり〜と思った」 = I was sure ～ (but I'd got it wrong) — three points: ① it carries the unspoken ‘got it wrong' — 「てっきり」 is “(I) was dead sure it was ～, but it wasn't,” with surprise/chagrin (てっきり来ると思ったのに来なかった), not a plain neutral “assumed”; ② 「てっきり」 is an adverb, always with 「と思った／思っていた」 (てっきり〜だと思った); ③ close to 「とばかり思っていた」 — both “dead sure yet wrong,” mostly interchangeable. This pattern is very common in everyday conversation — on realizing you were mistaken, 「てっきり〜と思ってた」 (I was sure ～) captures that “so I was wrong” surprise. It's often followed by a turn 「のに・が」 or the truth (実は〜), foregrounding the gap between “certainty vs fact.”

❓ Quick FAQ

Q: What's the difference between 「てっきり」 and a plain 「〜と思っていた (thought)」?

The difference is whether there's the unspoken ‘I got it wrong,' and the strength of certainty. 「てっきり〜と思った／思っていた」 = I was sure ～ (firmly certain at first, but got it wrong): 「てっきり」 carries strong certainty (dead sure, firmly believing), and the whole sentence almost always implies “but it wasn't, I was mistaken,” with surprise or chagrin: てっきり彼が来ると思っていたのに、来なかった (I was sure he'd come, but he didn't — certain yet wrong), てっきり今日だと思っていたが、明日だった (I was sure it was today, but it was tomorrow). Its focus is “(I was sure,) yet it turned out contrary to fact.” 「〜と思っていた」 = I (once) thought ～ (more neutral, not necessarily stressing being wrong): it just plainly states “(in the past) I thought this way,” not necessarily with “got it wrong,” nor stressing the strength of certainty: 昔は簡単だと思っていた (I used to think it was easy), 彼は来ると思っていた (I thought [then] he'd come — he may or may not have, neutral). It's more neutral, plain. Test: to stress “(I was dead sure it was ～,) but I got it wrong” (with surprise/chagrin) → てっきり〜と思った; to just say “(in the past) I thought ～” (neutral) → 〜と思っていた. E.g. on realizing a mix-up, 「てっきり明日だと思ってた (I was sure it was tomorrow — turns out it's today, with surprise)」 uses てっきり; plainly 「子供の頃はサンタがいると思っていた (as a child I thought Santa was real)」 uses と思っていた (a plain recollection). So 「てっきり」 is the intensified version of “thought,” carrying the unspoken ‘got it wrong' — almost always used in the chagrin/surprise context of “I was mistaken.”

Q: Does 「てっきり」 always need 「と思った」 after it? How can I use it?

Yes — 「てっきり」 is an adverb, almost always paired with a 「思う」-type verb like 「と思った／と思っていた／と信じていた／と思い込んでいた」 (assumed ～, believed ～), and can't stand alone. It modifies 「思う (assume),」 stressing “(I) assumed with dead certainty that ～.” Common pairings: ① てっきり〜と思った／思っていた (commonest): てっきり休みだと思っていた (I was sure it was a day off), てっきりあなたが担当だと思っていました (I was sure you were in charge); ② てっきり〜と思い込んでいた (stressing “firmly believed, dead sure”): てっきり成功すると思い込んでいた (I was dead sure it'd succeed [but it didn't]); ③ てっきり〜と信じていた: てっきり彼は独身だと信じていた (I firmly believed he was single [but he wasn't]). What follows is always a “(subjectively) assume, believe” verb like 思う／信じる／思い込む (in the past), because 「てっきり」 itself means “(I assumed it must be) ～.” So the test: seeing 「てっきり,」 「〜と思った／思っていた」 always follows, and the whole sentence implies “but it wasn't (I got it wrong).” It can't modify an action directly like a general adverb (× てっきり来た) — only “assume/believe.” Remember the fixed pairing “てっきり ＋ (plain form) ＋ と思った／思っていた” and you'll use it idiomatically.

🖊️ Practice Questions (5)

Q1. 「___晴れると思ったのに、雨が降った。」（I was sure it would be sunny）

(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) (I) assumed (they) were Japanese (but actually not)

(B) Certain (they) are Japanese

(C) Not sure whether or not

(D) Want to become Japanese

Q4. 「てっきり」の語感は?

(A) Firmly assumed something, but turned out to be wrong (unexpected)

(B) An objective fact

(C) A polite request

(D) A strong command

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。

Answer Explanations

1. (A) てっきり ── (I) assumed it would be sunny (but it rained).

2. (A) ── Must be paired with と思った/思っていた.

3. (A) ── (I) assumed (they) were Japanese (but actually not).

4. (A) ── Firmly assumed something, but turned out wrong.

5. (A) ── 「てっきり〜と思っていた」 is correct.