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Must be; without doubt
Definition
The grammar pattern "Plain form + に違いない / N・Na-adj (no だ) + に違いない" is used to express a strong conviction based on some evidence or logic. It indicates that something is certain or inevitable, and is often used in formal or written language. The pattern can be used with verbs in the plain form, as well as with Na-adjectives without the particle "だ". This expression is distinct from ～はずだ, which focuses on objective expectation, and should not be used in subjective emotional situations where ～に決まっている is more suitable.
Structure
| Form | Pattern | Example |
|---|---|---|
| Plain form | Verb + に違いない | 食べているから、彼はまだ起きているに違いない |
| Na-adjective | Na-adj + に違いない | この料理はとても美味しいに違いない |
| Noun | Noun + に違いない (Note: This is not a recommended usage) | 犯人はあの男に違いない (This usage is not recommended) |
Examples
明かりがついているから、彼はまだ起きているに違いない。
Akari ga tsuitte iru kara, kare wa mada okite iru ni chigainai.
The light is on, so he must still be awake.
明かりがついているから (The light is on because...)、彼はまだ起きている (he is still awake) に違いない (must be)
犯人はあの男に違いない。
Han'nin wa ano otoko ni chigainai.
The criminal must be that man.
犯人はあの男 (The criminal is that man) に違いない (must be)
これほど豪華な料理、材料費も高いに違いない。
Kore no hōka na ryōri, zairyōhi mo takai ni chigainai.
This kind of luxurious food must be expensive.
これほど豪華な料理 (This kind of luxurious food) 、材料費も高い (the material cost is also high) に違いない (must be)
Context
This pattern is used in formal or written language to express a strong conviction based on evidence or logic. It is distinct from ～はずだ, which focuses on objective expectation. In subjective emotional situations, ～に決まっている is more suitable.
Watch out
Using 'だ' with Nouns or Na-adjectives before に違いない is incorrect, as it changes the meaning of the sentence.
～はずだ focuses on objective expectation, while ～に違いない expresses a strong conviction based on evidence or logic.
～に決まっている is more suitable for subjective emotional situations, while ～に違いない is used for strong conviction based on evidence or logic.
Strategy
Pay attention to the context and the meaning of the sentence. Make sure to use the correct pattern and particles to express the intended meaning.
In context
Worked examples drawn from JLPT N2 test-style questions. Each sentence shows Plain form + に違いない / N・Na-adj (no だ) + に違いない used correctly, with a brief note on what the pattern is doing.
明かりがついているから、彼はまだ起きているに違いない。
Pattern used: に違いない
～に違いない is used for a strong guess based on evidence (the lights are on).
犯人はあの男に相違ない。
Pattern used: に相違ない
～に相違ない is the formal version used in reports or legal contexts; Nouns connect directly.
これほど豪華な料理、材料費も高いに違いない。
Pattern used: に違いない
Used to express a logical conclusion based on the observed luxury of the food.
Interactive
明かりがついているから、彼はまだ起きている______。
Adaptive practice
Our adaptive engine will quiz you on this grammar pattern and track your progress toward mastery.