正式 (seishiki) conjugation
official, formal
正式 (せいしき, seishiki) 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 | 正式だ seishikida | 正式です seishikidesu | The form you look up. Also the casual “is ~”. |
| Negative | 正式じゃない seishikijanai | 正式じゃないです seishikijanaidesu | “is not ~”. |
| Past | 正式だった seishikidatta | 正式でした seishikideshita | “was ~”. |
| Past negative | 正式じゃなかった seishikijanakatta | 正式じゃなかったです seishikijanakattadesu | “was not ~”. |
| Te-form | 正式で seishikide | — | Links to the next clause: “~ and …”. |
| Adverb | 正式に seishikini | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 正式な〜 seishikina〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 正式なら seishikinara | — | “if it is ~”. |
| Conditional (~たら) | 正式だったら seishikidattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 正式になる seishikininaru | 正式になります seishikininarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 正式すぎる seishikisugiru | 正式すぎます seishikisugimasu | “too ~”. |
| Looks ~ (~そう) | 正式そう seishikisou | 正式そうです seishikisoudesu | “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.