確か (tashika) conjugation
if I remember correctly; certain, definite
確か (たしか, tashika) 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 | 確かだ tashikada | 確かです tashikadesu | The form you look up. Also the casual “is ~”. |
| Negative | 確かじゃない tashikajanai | 確かじゃないです tashikajanaidesu | “is not ~”. |
| Past | 確かだった tashikadatta | 確かでした tashikadeshita | “was ~”. |
| Past negative | 確かじゃなかった tashikajanakatta | 確かじゃなかったです tashikajanakattadesu | “was not ~”. |
| Te-form | 確かで tashikade | — | Links to the next clause: “~ and …”. |
| Adverb | 確かに tashikani | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 確かな〜 tashikana〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 確かなら tashikanara | — | “if it is ~”. |
| Conditional (~たら) | 確かだったら tashikadattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 確かになる tashikaninaru | 確かになります tashikaninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 確かすぎる tashikasugiru | 確かすぎます tashikasugimasu | “too ~”. |
| Looks ~ (~そう) | 確かそう tashikasou | 確かそうです tashikasoudesu | “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.