清潔 (seiketsu) conjugation
clean
清潔 (せいけつ, seiketsu) 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 | 清潔だ seiketsuda | 清潔です seiketsudesu | The form you look up. Also the casual “is ~”. |
| Negative | 清潔じゃない seiketsujanai | 清潔じゃないです seiketsujanaidesu | “is not ~”. |
| Past | 清潔だった seiketsudatta | 清潔でした seiketsudeshita | “was ~”. |
| Past negative | 清潔じゃなかった seiketsujanakatta | 清潔じゃなかったです seiketsujanakattadesu | “was not ~”. |
| Te-form | 清潔で seiketsude | — | Links to the next clause: “~ and …”. |
| Adverb | 清潔に seiketsuni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 清潔な〜 seiketsuna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 清潔なら seiketsunara | — | “if it is ~”. |
| Conditional (~たら) | 清潔だったら seiketsudattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 清潔になる seiketsuninaru | 清潔になります seiketsuninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 清潔すぎる seiketsusugiru | 清潔すぎます seiketsusugimasu | “too ~”. |
| Looks ~ (~そう) | 清潔そう seiketsusou | 清潔そうです seiketsusoudesu | “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.