に相違ない|にそういない
Expresses the speaker's strong conviction that something is certainly true, based on some grounds; 'must be', 'there is no doubt that'. It is a formal, written-style equivalent of に違いない.
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Used mainly in writing, such as novels, essays, reports and formal speeches, to state a confident judgment the speaker reaches from evidence or observation. It carries the same meaning as に違いない but sounds stiffer and more literary, so it is rarely heard in casual conversation.
Do not put だ directly before に相違ない; say 犯人である に相違ない or 犯人 に相違ない, not 犯人だに相違ない.
Learners should avoid it in casual speech, where it sounds overly stiff; に違いない is the natural everyday choice.
Note that it expresses the speaker's own conviction, not a proven fact or a generally accepted view.
- に違いないN3「に違いない」 means essentially the same thing but is stylistically neutral, used in both speech and writing, with the polite form 「に違いありません」. The two are interchangeable in writing, but 「に違いない」 is the better choice in everyday conversation.
- に決まっているN2「に決まっている」 is conversational and rests on common sense or subjective conviction; it sounds emphatic and is often followed by 「よ」 or 「じゃない」. Besides asserting an outcome, it can stress that something is a matter of course ("it goes without saying"), and it is generally not used in place of 「に相違ない」 in written prose.
- はずだN4「はずだ」 infers what "should" be the case from reasons or common sense, with less certainty than 「に相違ない」, and is common in both speech and writing; 「はずだった」 can also express an expectation that fell through. Nouns connect with 「の」 and な-adjectives with 「な」.
- ものと思われるN1「ものと思われる」 is a hedged, tentative guess ("presumably...") that uses 「思われる」 to tone down subjectivity; its certainty is far lower than 「に相違ない」, so the two are not interchangeable. Nouns and な-adjectives usually need 「である」 before it.
- とされるN1「に相違ない」 expresses the speaker's own strong conviction, whereas 「とされる」 reports views or presumptions prevailing in society or academia, or states that something is classified as such by regulation. Because 「とされる」 does not represent the speaker's judgment, the two are not interchangeable.
に相違ない means the same as に違いない but is more formal and written, while に決まっている is a colloquial, emphatic assertion, and はずだ marks a logical expectation derived from facts. ものと思われる is a hedged, less certain formal judgment, and とされる reports a general or official view rather than the speaker's own conviction.
