誠実 (seijitsu) conjugation
sincere, honest, faithful
誠実 (せいじつ, seijitsu) 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 | 誠実だ seijitsuda | 誠実です seijitsudesu | The form you look up. Also the casual “is ~”. |
| Negative | 誠実じゃない seijitsujanai | 誠実じゃないです seijitsujanaidesu | “is not ~”. |
| Past | 誠実だった seijitsudatta | 誠実でした seijitsudeshita | “was ~”. |
| Past negative | 誠実じゃなかった seijitsujanakatta | 誠実じゃなかったです seijitsujanakattadesu | “was not ~”. |
| Te-form | 誠実で seijitsude | — | Links to the next clause: “~ and …”. |
| Adverb | 誠実に seijitsuni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 誠実な〜 seijitsuna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 誠実なら seijitsunara | — | “if it is ~”. |
| Conditional (~たら) | 誠実だったら seijitsudattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 誠実になる seijitsuninaru | 誠実になります seijitsuninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 誠実すぎる seijitsusugiru | 誠実すぎます seijitsusugimasu | “too ~”. |
| Looks ~ (~そう) | 誠実そう seijitsusou | 誠実そうです seijitsusoudesu | “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.