“〜ni kimatte iru”: It's Bound to Be 〜 / Of Course 〜 (a strong subjective assertion) [JLPT N2]

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

“He's bound to be the culprit” — an assertion with strong subjective conviction

「そんなの、嘘に決まってる!」 — no need to think, it's surely so

Hearing a fishy claim, you blurt out 「そんなの、嘘に決まってる!」 (that's surely a lie!) — 「〜に決まっている」 = it's surely ～, of course ～, carrying a strong subjective conviction, asserting “no doubt it's so, no need even to think.” It's the assertion “that goes without saying” in speech. This guide covers its subjective-conviction feel and how to tell it from 「に違いない」「はずだ.」

Core: subjectively convinced ‘of course, surely it's so'

「plain form ＋ に決まっている」 means “(the speaker is convinced) it's surely ～, of course ～, no doubt ～”:

• 彼が犯人に決まっている (he's surely the culprit).
• そんな話、嘘に決まっている (a story like that is of course a lie).
• 練習すれば、上手くなるに決まっている (if you practice, of course you'll get good).

Feel: “it's surely ～, of course ～, that goes without saying” — the core is that the speaker is subjectively convinced beyond doubt, asserting “no need to think, it's surely so.” It carries a strong subjective conviction (not necessarily with objective grounds, but the speaker “takes it as certain”), often with a “that goes without saying, obviously” tone. Very common in speech (colloquially 「〜に決まってる」).

How it attaches

Example sentences

• こんなに練習したんだから、勝てるに決まっている。(After practicing this much, of course we can win.)
• 徹夜で作業すれば、体を壊すに決まっている。(Work all night and of course you'll ruin your health.)
• 「この店、おいしいかな?」「行列ができてるんだから、おいしいに決まってるよ」(“Is this place good?” “There's a queue, so of course it's good.”)
• 一人でそんな大金を用意するなんて、無理に決まっている。(Preparing that much money alone is of course impossible.)
• 子供がそんな時間に外にいたら、危ないに決まっている。(A child out at that hour is of course in danger.)

⚠️ Where learners slip up

① It expresses ‘strong subjective conviction,' with a ‘that goes without saying' tone. 「に決まっている」's core is that the speaker is subjectively convinced beyond doubt, takes it as certain that “it's surely so,” with a “that goes without saying, no need to think, obviously” tone. It doesn't necessarily have objective grounds — it's the speaker's strong assertion “(I) take it as certain, no doubt”: そんなの嘘に決まってる (that's of course a lie — the speaker is convinced), 努力すれば成功するに決まっている (of course you succeed if you try, that goes without saying). So it carries a subjective, categorical feel, often for rebuttal, stressing the obvious, expressing strong conviction. It corresponds to “it's surely ～, of course ～, definitely ～, that goes without saying.” Note it's the subjective conviction of “(I) take it as certain,” with a very strong, categorical tone (sometimes even a bit forced).

② Nouns and な-adjectives attach directly, without 「だ.」 Note the attachment. With a noun or な-adjective, attach 「に決まっている」 directly, without 「だ」: ○ 嘘に決まっている (noun, of course a lie) / × 嘘だに決まっている (× adding だ wrong), ○ 無理に決まっている (な-adj, of course impossible) / × 無理だに決まっている. With a verb or い-adjective, attach the plain form directly: 勝つに決まっている (verb), 高いに決まっている (い-adj). Mnemonic: noun/な-adj attach directly (no だ), verb/い-adj attach the plain form. (Note that before the 「に」 of 「に決まっている,」 a noun/な-adjective attaches directly.)

③ 「に決まっている」 vs 「に違いない」: subjective conviction vs grounded inference. Both express “it must be ～,” but the nature of the conviction differs. 「〜に決まっている」 = it's surely ～ (a strong subjective conviction, assertion): the speaker subjectively takes it as certain “of course it's so,” with the categorical “that goes without saying,” not necessarily with objective grounds, a strong tone: 彼が嘘をついてるに決まってる (he's surely lying — subjective certainty). 「〜に違いない」 = it must be ～ (a grounded strong inference): a strong inference based on some clues, grounds, more objective, more grounded: 足音がする。誰かいるに違いない (there are footsteps; someone must be there — inferring from a clue). Difference: 「に決まっている」 leans subjective assertion “of course, that goes without saying” (the speaker takes it as certain); 「に違いない」 leans grounded inference “it must be” (judging from clues). Test: to subjectively assert “of course it's ～, that goes without saying” → に決まっている (colloquial, subjective, categorical); to infer from clues “it must be ～” → に違いない (more objective, grounded).

🔄 Compare: に決まっている／に違いない／はずだ／きっと

💡 How to remember this

「〜に決まっている」 = it's surely ～, of course ～, carrying a strong subjective conviction — three points: ① subjectively convinced ‘that goes without saying, no need to think' — the speaker takes it as certain “of course it's so,” with a categorical tone (not necessarily objectively grounded), colloquially contracting to 「〜に決まってる」; ② nouns and な-adj attach directly, without 「だ」 (嘘に決まっている, 無理に決まっている); ③ separate it from 「に違いない」 — に決まっている leans subjective assertion “of course” (that goes without saying), に違いない leans grounded inference “it must be” (from clues). This pattern is very colloquial, common for rebuttal or stressing the obvious — 「そんなの〜に決まってる (that's of course ～)」 expresses strong conviction in one line. But since the tone is categorical, mind the setting (weigh it when asserting to elders/in formal settings).

❓ Questions you might have

Q: 「に決まっている」 and 「に違いない」 both mean ‘it must be ～' — what's the difference?

The difference is the ‘nature' of the conviction — subjective certainty vs grounded inference. 「〜に決まっている」 = it's surely ～, of course ～ (a strong subjective conviction, assertion): the speaker subjectively takes it as certain “of course it's so, no doubt,” with the categorical tone of “that goes without saying, no need to think, obviously,” not necessarily with objective grounds — just “(I) am convinced”: そんなの嘘に決まってる (that's of course a lie — subjective certainty), こんなに努力したんだから、受かるに決まっている (after trying this hard, of course I'll pass — an obvious assertion). It leans subjective, categorical (sometimes with a “no argument” feel). 「〜に違いない」 = it must be ～ (a strong inference from clues/grounds): based on concrete clues, signs, grounds, a strong inference “it must be ～,” more objective, grounded: 部屋の電気がついている。誰かいるに違いない (the room light is on; someone must be there — inferring from the “light on” clue), 彼の表情から見て、何か隠しているに違いない (from his expression, he must be hiding something — inferring from signs). It leans grounded inference (I judge from clues that “it must be”). Difference: 「に決まっている」 is a subjective assertion “of course, that goes without saying” (the speaker takes it as certain, not necessarily grounded); 「に違いない」 is a grounded inference “it must be” (judging from clues). Test: to subjectively, categorically say “of course it's ～, that goes without saying” → に決まっている (colloquial, strong conviction); to infer from clues “it must be ～” → に違いない (more objective, grounded). E.g. 「行列ができてるんだから、おいしいに決まってる (there's a queue, so of course it's good — subjective assertion)」 uses に決まっている; 「靴が濡れている。外は雨に違いない (my shoes are wet; it must be raining outside — from a clue)」 uses に違いない. One subjective certainty, one grounded inference.

Q: Does a noun before 「に決まっている」 take 「だ」?

No 「だ」 — a noun attaches to 「に決まっている」 directly. In attachment, both nouns and な-adjectives attach 「に決まっている」 directly, without 「だ」:

• Noun: ○ 嘘に決まっている (of course a lie), ○ 彼が犯人に決まっている (he's surely the culprit) / × 嘘だに決まっている, × 犯人だに決まっている (adding だ is wrong)
• な-adjective: ○ 無理に決まっている (of course impossible), ○ 危険に決まっている (of course dangerous) / × 無理だに決まっている, × 危険だに決まっている

While verbs and い-adjectives attach the plain form directly:

• Verb: 勝つに決まっている (of course we'll win), 来るに決まっている (of course they'll come)
• い-adjective: 高いに決まっている (of course expensive), おいしいに決まっている (of course tasty)

So the rule: noun・な-adjective → attach に決まっている directly (no だ); verb・い-adjective → attach the plain form. The easiest error is noun/な-adj — don't add 「だ」 (× 嘘だに決まっている → ○ 嘘に決まっている). This is because the 「に」 of 「に決まっている」 attaches directly to a noun (noun ＋ に ＋ 決まっている), with no 「だ」 in between. Colloquially it often contracts to 「〜に決まってる」 (嘘に決まってる, 無理に決まってる). Remember “noun/な-adj no だ, attach に決まっている directly” and you won't misattach.

🖊️ Practice Questions (5)

Q1. 「こんな簡単な問題、できる___。」(of course can do it; naturally)

(A) に決まっている　(B) わけがない　(C) おそれがある　(D) かねない

Q2. 「に決まっている」(名詞)の接法は?

(A) 名詞＋に決まっている (without adding だ)　(B) 名詞＋だに決まっている　(C) 名詞＋なに決まっている　(D) 名詞＋のに決まっている

Q3. 「嘘に決まっている」の意味は?

(A) Surely a lie (strong subjective conviction)

(B) Maybe a lie

(C) Not a lie

(D) Asking whether it's a lie

Q4. 「に決まっている」の語感は?

(A) Strong subjective conviction (a matter of course)

(B) Merely/nothing but

(C) Might well happen

(D) Have no choice but to

Q5. 接法が正しいのは?

(A) 便利に決まっている。　(B) 便利だに決まっている。

(C) 便利なに決まっている。　(D) 便利をに決まっている。

Answer Explanations

1. (A) に決まっている ── Of course can do it (a matter of course).

2. (A) ── A noun attaches directly ＋ に決まっている.

3. (A) ── Surely a lie (strong conviction).

4. (A) ── Strong subjective conviction.

5. (A) ── The na-adjective stem attaches directly ＋ (便利に決まっている).