不可欠 (fukaketsu) conjugation
indispensable, essential
不可欠 (ふかけつ, fukaketsu) is a na-adjective. Na-adjectives behave like nouns. The word itself never changes — you conjugate だ/です after it, and you need な to put it in front of a noun.
Conjugation table
| Form | Plain (casual) | Polite (~です) | When you use it |
|---|---|---|---|
| Dictionary / plain | 不可欠だ fukaketsuda | 不可欠です fukaketsudesu | The form you look up. Also the casual “is ~”. |
| Negative | 不可欠じゃない fukaketsujanai | 不可欠じゃないです fukaketsujanaidesu | “is not ~”. |
| Past | 不可欠だった fukaketsudatta | 不可欠でした fukaketsudeshita | “was ~”. |
| Past negative | 不可欠じゃなかった fukaketsujanakatta | 不可欠じゃなかったです fukaketsujanakattadesu | “was not ~”. |
| Te-form | 不可欠で fukaketsude | — | Links to the next clause: “~ and …”. |
| Adverb | 不可欠に fukaketsuni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 不可欠な〜 fukaketsuna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 不可欠なら fukaketsunara | — | “if it is ~”. |
| Conditional (~たら) | 不可欠だったら fukaketsudattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 不可欠になる fukaketsuninaru | 不可欠になります fukaketsuninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 不可欠すぎる fukaketsusugiru | 不可欠すぎます fukaketsusugimasu | “too ~”. |
| Looks ~ (~そう) | 不可欠そう fukaketsusou | 不可欠そうです fukaketsusoudesu | “looks / seems ~” from appearance. |
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Why it conjugates this way
Na-adjectives behave like nouns. The word itself never changes — you conjugate だ/です after it, and you need な to put it in front of a noun.
See the full rules in the adjective conjugation guide.