急速 (kyuusoku) conjugation
rapid (e.g., progress)
急速 (きゅうそく, kyuusoku) 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 | 急速だ kyuusokuda | 急速です kyuusokudesu | The form you look up. Also the casual “is ~”. |
| Negative | 急速じゃない kyuusokujanai | 急速じゃないです kyuusokujanaidesu | “is not ~”. |
| Past | 急速だった kyuusokudatta | 急速でした kyuusokudeshita | “was ~”. |
| Past negative | 急速じゃなかった kyuusokujanakatta | 急速じゃなかったです kyuusokujanakattadesu | “was not ~”. |
| Te-form | 急速で kyuusokude | — | Links to the next clause: “~ and …”. |
| Adverb | 急速に kyuusokuni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 急速な〜 kyuusokuna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 急速なら kyuusokunara | — | “if it is ~”. |
| Conditional (~たら) | 急速だったら kyuusokudattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 急速になる kyuusokuninaru | 急速になります kyuusokuninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 急速すぎる kyuusokusugiru | 急速すぎます kyuusokusugimasu | “too ~”. |
| Looks ~ (~そう) | 急速そう kyuusokusou | 急速そうです kyuusokusoudesu | “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.