有益 (yuueki) conjugation
beneficial, profitable
有益 (ゆうえき, yuueki) 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 | 有益だ yuuekida | 有益です yuuekidesu | The form you look up. Also the casual “is ~”. |
| Negative | 有益じゃない yuuekijanai | 有益じゃないです yuuekijanaidesu | “is not ~”. |
| Past | 有益だった yuuekidatta | 有益でした yuuekideshita | “was ~”. |
| Past negative | 有益じゃなかった yuuekijanakatta | 有益じゃなかったです yuuekijanakattadesu | “was not ~”. |
| Te-form | 有益で yuuekide | — | Links to the next clause: “~ and …”. |
| Adverb | 有益に yuuekini | — | Turns it into “~ly”, describing a verb. |
| Before a noun | 有益な〜 yuuekina〜 | — | How it attaches when it modifies a noun. |
| Conditional (~ば/なら) | 有益なら yuuekinara | — | “if it is ~”. |
| Conditional (~たら) | 有益だったら yuuekidattara | — | “if / when it is ~”. The everyday conditional. |
| Become (~なる) | 有益になる yuuekininaru | 有益になります yuuekininarimasu | “becomes ~” — the change-of-state form. |
| Too much (~すぎる) | 有益すぎる yuuekisugiru | 有益すぎます yuuekisugimasu | “too ~”. |
| Looks ~ (~そう) | 有益そう yuuekisou | 有益そうです yuuekisoudesu | “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.