に違いない

Must Be

Level 2Sounds Like nichigainai

に違いない（にちがいない） is used when you are very confident about a conclusion based on evidence or logic. It translates to 'must be,' 'no doubt,' or 'certainly.'

How It Works

に違いない is a powerful way to express certainty. It literally means 'there is no mistake' (違い（ちがい） = mistake/difference; ない = non-existent).

1. Usage Nuance
It is used when you see or hear something and draw a logical conclusion. For example, if you see someone wearing a very expensive watch, you might say 'He must be rich.' It is more subjective than はず, which relies on objective schedules or rules. To strengthen the conviction, it is frequently paired with the adverb きっと (surely) at the start of the sentence.

2. Conjugation Rules

  • Verbs: Use the plain form (e.g., 行く, 食べた).
  • い-Adjectives: Use the plain form (e.g., 高い, 寒かった).
  • な-Adjectives: For present tense, use the stem only (e.g., 暇に違いない). For past tense, use だった (e.g., 暇だったに違いない).
  • Nouns: For present tense, use the noun directly (e.g., 犯人に違いない). For past tense, use だった (e.g., 犯人だったに違いない).

3. Formality
In polite speech, you can add です to the end: に違いないです. However, the standard polite version used in formal speech and presentations is に違いありません. In formal writing or legal contexts, the variant に相違ない is used.

Examples (4)

  1. 彼は犯人に違いない。

    He must be the culprit.

    Word by Word: He (topic) culprit to no-mistake.

    Based on the evidence available, the speaker is strongly convinced that he is the one who did it.

  2. あんなに働いたら、疲れているに違いない。

    After working that much, he must be tired.

    Word by Word: That much if worked, tired-being to no-mistake.

    This uses the ている form to show a current state resulting from a previous action.

  3. このレストランはいつも混んでいるから、美味しいに違いない。

    This restaurant is always crowded, so it must be delicious.

    Word by Word: This restaurant (topic) always crowded-being because, delicious to no-mistake.

    The speaker uses the evidence of the crowd to infer the quality of the food.

  4. 明日は雨に違いない。

    It will certainly rain tomorrow.

    Word by Word: Tomorrow (topic) rain to no-mistake.

    Note that for nouns like 雨（あめ）, we do not use the copula 'da' before the pattern.

Common Mistakes

  • Including the copula 'da' with nouns or na-adjectives in the present tense.

    彼は学生だに違いない。
    彼は学生に違いない。

    Unlike some other patterns, you must drop the だ when attaching に違いない to nouns or な-adjectives for present tense deductions.

  • Confusing it with the verb 違う（ちがう）.

    答えが違いない。
    答えが違わない。

    If you want to say 'the answer is not different/wrong' as a simple verb negation, use 違わない（ちがわない）. に違いない is a fixed expression for 'must be' and requires the particle に.

  • Using the present form for past tense deductions.

    昨日の犯人は彼に違いない。
    昨日の犯人は彼だったに違いない。

    When making a deduction about a past state for nouns or な-adjectives, you must use the past form だった before に違いない.

How It Connects

Tap a pattern to see what it builds on and what it leads to.

に違いないLevel 2Must Be

Learn This First

To understand 'に違いない' (must be), you need to be familiar with the particle 'に' and the basic copula 'だ', as this pattern acts as a strong, evidence-based assertion. You should also understand how to connect nouns, adjectives, and verbs to following expressions.

Words in This Pattern

違いない