ありえない・あり得ない・有り得ないarienai

1. i-adjectiveimpossible
   それは決けっしてありえない。↗

   That'll be a cold day in hell.
2. i-adjectiveunthinkable; unbelievable; ridiculous; absurd

• Synonym不可能ふかのうNeutralStates impossibility objectively, as in 「実現不可能」; neutral, often in writing, and carries none of the exclamatory tone of 「ありえない」.
• Synonym不能ふのうWrittenWritten and formal: unable to do something, mostly used as a suffix, as in 「再起不能」「修復不能」「使用不能」.
• Related無理むりNeutralFrequent in speech, as in 「無理です」: something is unmanageable or can't be done, focusing on inability rather than logical impossibility.
• Relatedとんでも無いとんでもないNeutralCovers the outrageous and absurd, and doubles as the polite set phrase 「とんでもない」; its range of uses is broad.
• Related及び難いおよびがたいWrittenWritten and formal: hard to attain, stressing the gap to be closed, as in 「及び難い境地」.
• Related絶望的ぜつぼうてきNeutralMeans hopeless, stressing a bleak outlook; it describes dire situations rather than exclaiming at something absurd.
• Related非現実的ひげんじつてきNeutralMeans unrealistic, leaning toward written style, as in 「非現実的な計画」.
• RelatedインポシブルNeutralA loanword for impossible; very rare in everyday speech and mostly met in titles.
• Related考えられないかんがえられないNeutralMeans unthinkable or hard to imagine, as in 「考えられないミス」; it stresses the speaker's surprise.
• Antonymあり得るありうるNeutralThe antonym: possible or conceivable, as in 「十分ありうる話」.

Use 「ありえない」 for logical impossibility or as a colloquial exclamation at something outrageous, as in 「ありえない！」. To state impossibility objectively, pick 「不可能」; for something you simply can't manage, 「無理」. 「あり得る」 is the antonym.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. それが起おきる可能性かのうせいが無ない。存在そんざいしえない。
2. （通常つうじょう悪わるい意味いみで）信しんじられない。あってはならない。