是非|ぜひzehi[1]atamadaka (head-high)

1. adverbcertainly; without fail
   「キャッチボールしようか」「よし、是非ぜひやろう」↗

   "How about playing catch?" "Sure, why not?"
2. nounright and wrong; pros and cons

• Synonym是非ともぜひともWrittenAn emphatic 「是非」: 'no matter what, absolutely must'. More earnest and insistent than the headword.
• Synonym必ずかならずNeutralCenters on certainty: that something will surely happen or be done without fail. 「是非」 centers instead on voicing a wish or urging.
• Synonym何卒なにとぞFormalFormal, deferential 'please' for earnest requests, as in 「何卒よろしくお願いします」; typical of letters and business writing.
• SynonymどうしてもCasual'No matter what' — resolve to do something regardless; with a negative, it means something just cannot be, however hard one tries.
• SynonymどうぞNeutralA plain 'please' or 'go ahead' for inviting or permitting; 「是非」 urges with more earnestness.
• SynonymぜひぜひCasualDoubled 「是非」 for extra emphasis; warm and eager, even a little coaxing, as in 「ぜひぜひ来てね」.
• Synonym何が何でもなにがなんでもCasual'At all costs' — a strong resolve to get it done come what may; more determined and forceful than 「是非」.
• Synonym必ずやかならずやWrittenWritten-language 'surely, certainly'; more formal and dignified than 「必ず」.
• Synonym理が非でもりがひでもWrittenIdiom meaning 'by fair means or foul' — forcing something through without regard to right or wrong.
• Related断じてだんじてWrittenWritten-style 'absolutely, decidedly'; usually with a negative, as in 「断じて許さない」.
• Related雨が降ろうと槍が降ろうとあめがふろうとやりがふろうとCasualIdiom, 'come hell or high water': a vow to see it through whatever happens, with exaggerated determination.

Use 「是非」 to express a wish or urging, as in 「是非来てください」. For a more earnest plea, 「是非とも」; for formal requests, 「何卒」. 「必ず」 states certainty that something will happen; 「どうしても」 and 「何が何でも」 add a 'no matter what' resolve.

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

1. 正ただしいことと正ただしくないこと。
2. 物事ものごとの良し悪よしあしを論ろんじること。
3. 物事ものごとの実現じつげん・実行じっこうを強つよく希望きぼうする様さま。
4. ある条件じょうけん下かにおいては必かならずその結果けっかが得えられると判断はんだんできるさま。