正当 (seitou) conjugation
just, due, proper
正当 (せいとう, seitou) 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 | 正当だ seitouda | 正当です seitoudesu | The form you look up. Also the casual “is ~”. |
| Negative | 正当じゃない seitoujanai | 正当じゃないです seitoujanaidesu | “is not ~”. |
| Past | 正当だった seitoudatta | 正当でした seitoudeshita | “was ~”. |
| Past negative | 正当じゃなかった seitoujanakatta | 正当じゃなかったです seitoujanakattadesu | “was not ~”. |
| Te-form | 正当で seitoude | — | Links to the next clause: “~ and …”. |
| Adverb | 正当に seitouni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 正当な〜 seitouna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 正当なら seitounara | — | “if it is ~”. |
| Conditional (~たら) | 正当だったら seitoudattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 正当になる seitouninaru | 正当になります seitouninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 正当すぎる seitousugiru | 正当すぎます seitousugimasu | “too ~”. |
| Looks ~ (~そう) | 正当そう seitousou | 正当そうです seitousoudesu | “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.