熱心 (nesshin) conjugation
enthusiasm
熱心 (ねっしん, nesshin) 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 | 熱心だ nesshinda | 熱心です nesshindesu | The form you look up. Also the casual “is ~”. |
| Negative | 熱心じゃない nesshinjanai | 熱心じゃないです nesshinjanaidesu | “is not ~”. |
| Past | 熱心だった nesshindatta | 熱心でした nesshindeshita | “was ~”. |
| Past negative | 熱心じゃなかった nesshinjanakatta | 熱心じゃなかったです nesshinjanakattadesu | “was not ~”. |
| Te-form | 熱心で nesshinde | — | Links to the next clause: “~ and …”. |
| Adverb | 熱心に nesshinni | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 熱心な〜 nesshinna〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 熱心なら nesshinnara | — | “if it is ~”. |
| Conditional (~たら) | 熱心だったら nesshindattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 熱心になる nesshinninaru | 熱心になります nesshinninarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 熱心すぎる nesshinsugiru | 熱心すぎます nesshinsugimasu | “too ~”. |
| Looks ~ (~そう) | 熱心そう nesshinsou | 熱心そうです nesshinsoudesu | “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.