害する (gaisuru) conjugation
to harm, to offend
害する (がいする, gaisuru) is an irregular verb. Only する and 来る are truly irregular, and every learner meets them in week one. Every form below is tappable — hear it, then say it back.
Conjugation table
| Form | Plain (casual) | Polite (~ます) | When you use it |
|---|---|---|---|
| Dictionary / plain | 害する gaisuru | 害します gaishimasu | The form you look up. Also the casual present and future. |
| Plain negative | 害しない gaishinai | 害しません gaishimasen | “doesn’t / won’t”. From here it conjugates like an i-adjective. |
| Plain past | 害した gaishita | 害しました gaishimashita | The casual past — same ending as the te-form, with た/だ. |
| Plain past negative | 害しなかった gaishinakatta | 害しませんでした gaishimasendeshita | “didn’t”. The negative past, still i-adjective-shaped. |
| Te-form | 害して gaishite | — | The connector: requests, linking clauses, ~ている. |
| Progressive (~ている) | 害している gaishiteiru | 害しています gaishiteimasu | “is ~ing”, or an ongoing resulting state. |
| Desire (~たい) | 害したい gaishitai | 害したいです gaishitaidesu | “want to ~”. Behaves as an i-adjective. |
| Volitional | 害しよう gaishiyou | 害しましょう gaishimashou | “let’s ~” / “I think I’ll ~”. |
| Potential | 害できる gaidekiru | 害できます gaidekimasu | “can ~”. What you could do; the object often takes が. |
| Passive | 害される gaisareru | 害されます gaisaremasu | “is ~ed”. Also the honorific and the suffering passive. |
| Causative | 害させる gaisaseru | 害させます gaisasemasu | Make or let someone do it. |
| Causative-passive | 害させられる gaisaserareru | 害させられます gaisaseraremasu | Be made to do it — the long one. |
| Imperative | 害しろ gaishiro | 害してください gaishitekudasai | Blunt order. Use ~てください in real life. |
| Prohibitive | 害するな gaisuruna | — | “don’t!” — dictionary form + な. |
| Conditional (~ば) | 害すれば gaisureba | — | “if ~”. General rules and hypotheticals. |
| Conditional (~たら) | 害したら gaishitara | — | “if / when ~”. The everyday conditional. |
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Why it conjugates this way
Only する and 来る are truly irregular, and every learner meets them in week one.
See the full rules on the verb conjugation guide.