こする (kosuru) conjugation
to rub, to chafe, to file, to frost (glass), to strike (match)
こする (こする, kosuru) is a godan verb. Godan verbs change their final kana up and down its column of the kana chart — the a-row for negatives, the i-row before ます, the e-row for potential and ば. Every form below is tappable — hear it, then say it back.
Written 擦る in kanji, but usually written in kana alone.
Conjugation table
| Form | Plain (casual) | Polite (~ます) | When you use it |
|---|---|---|---|
| Dictionary / plain | こする kosuru | こすります kosurimasu | The form you look up. Also the casual present and future. |
| Plain negative | こすらない kosuranai | こすりません kosurimasen | “doesn’t / won’t”. From here it conjugates like an i-adjective. |
| Plain past | こすった kosutta | こすりました kosurimashita | The casual past — same ending as the te-form, with た/だ. |
| Plain past negative | こすらなかった kosuranakatta | こすりませんでした kosurimasendeshita | “didn’t”. The negative past, still i-adjective-shaped. |
| Te-form | こすって kosutte | — | The connector: requests, linking clauses, ~ている. |
| Progressive (~ている) | こすっている kosutteiru | こすっています kosutteimasu | “is ~ing”, or an ongoing resulting state. |
| Desire (~たい) | こすりたい kosuritai | こすりたいです kosuritaidesu | “want to ~”. Behaves as an i-adjective. |
| Volitional | こすろう kosurou | こすりましょう kosurimashou | “let’s ~” / “I think I’ll ~”. |
| Potential | こすれる kosureru | こすれます kosuremasu | “can ~”. What you could do; the object often takes が. |
| Passive | こすられる kosurareru | こすられます kosuraremasu | “is ~ed”. Also the honorific and the suffering passive. |
| Causative | こすらせる kosuraseru | こすらせます kosurasemasu | Make or let someone do it. |
| Causative-passive | こすらされる kosurasareru | こすらされます kosurasaremasu | Be made to do it — the long one. |
| Imperative | こすれ kosure | こすってください kosuttekudasai | Blunt order. Use ~てください in real life. |
| Prohibitive | こするな kosuruna | — | “don’t!” — dictionary form + な. |
| Conditional (~ば) | こすれば kosureba | — | “if ~”. General rules and hypotheticals. |
| Conditional (~たら) | こすったら kosuttara | — | “if / when ~”. The everyday conditional. |
🔊 Tap any Japanese word to hear it spoken.
Why it conjugates this way
Godan verbs change their final kana up and down its column of the kana chart — the a-row for negatives, the i-row before ます, the e-row for potential and ば.
See the full rules on the verb conjugation guide.