わけがない

Expresses the speaker's strong conviction, based on reasoning or common sense, that something is impossible or out of the question: "there's no way that…", "it can't be that…".

Used in everyday conversation and writing to reject a possibility firmly, often with emotional emphasis, as when defending someone or dismissing an idea. It is close to はずがない but sounds more subjective and emphatic. The casual form わけない is common in speech.

• はずがないN4「はずがない」 also means 'impossible' and in most cases can be swapped with 「わけがない」. It emphasizes inference from reasons, common sense, or known facts and sounds calmer, while 「わけがない」 is more subjective and emotionally charged.
• っこないN2「っこない」 has a similar meaning but attaches only to the ます形 of verbs and is often used with potential verbs; it is very casual spoken language with an even stronger subjective tone, and is generally avoided in formal situations and writing. In speech, when attached to verbs, it can often be used interchangeably with 「わけがない」.
• わけではないN3「わけではない」 means 'it is not that ...', softly denying an inference or claim, and it can combine with 「すべて」 and similar words to express partial negation; it does not mean 'impossible', so the two cannot be swapped. When attaching to a noun, use 「な／である」, not 「の」.
• ものかN2When denying a possibility, 「ものか」 is close to 「わけがない」 but more emotional and mostly used in speech; it can also express a determined refusal ('never ...'), and in that usage the two cannot be swapped. With nouns it takes 「な」: 「先生なものか」.
• わけにはいかないN3「わけがない」 asserts that something cannot possibly be the case and can attach to many kinds of words, while 「わけにはいかない」 means being unable to do something out of social propriety and attaches only to the 辞書形 or ない形 of verbs — with the ない形 it means 'cannot not do' (must do). The two are not interchangeable.
• はずだN4「はずだ」 is an evidence-based affirmative conjecture ('should ...'), while 「わけがない」 is a strong negation ('impossible'), so the two are not interchangeable. To express 'impossible' you can use 「はずがない」, but it is less subjective and emphatic than 「わけがない」.

はずがない also denies a possibility but sounds more objective and grounds-based. っこない is a more colloquial denial attached to the verb ます-stem, and ものか is an emotional rhetorical denial or refusal that often expresses the speaker's will; わけではない is a partial negation ("it's not that…"), わけにはいかない means one cannot do something for social or moral reasons, and はずだ is the affirmative "should be / is expected to".