する（to do）is the single most frequent verb in the language, and it is irregular — one of only two truly irregular verbs, alongside 来る. It cannot be conjugated by any rule; you memorize the whole paradigm as a unit. The reason it feels slippery is that its stem is not fixed the way a 一段 stem is: it shifts between し, せ, and す depending on the form, and its potential is a completely different word, できる. Learn this one table and you unlock thousands of verbs, because every noun + する compound (勉強する, 電話する, 予約する…) conjugates on this exact する.
The full paradigm
| Form (Japanese term) | する | Reading | Stem |
|---|---|---|---|
| Dictionary (辞書形) | する | suru | す |
| Polite (ます形) | します | shimasu | し |
| Negative (ない形) | しない | shinai | し |
| Past (た形) | した | shita | し |
| te-form (て形) | して | shite | し |
| Potential (可能形) | できる | dekiru | — (suppletive) |
| Passive (受身形) | される | sareru | さ |
| Causative (使役形) | させる | saseru | さ |
| Volitional (意向形) | しよう | shiyō | し |
| Conditional (仮定形・ば) | すれば | sureba | す |
| Imperative (命令形) | しろ／せよ | shiro / seyo | し／せ |
The し-stem forms in real use
週末は特に何もしない。
shūmatsu wa toku ni nani mo shinai
I'm not really doing anything this weekend.
心配しないで。すぐ終わるから。
shinpai shinaide. sugu owaru kara
Don't worry — it'll be over soon.
昨日、久しぶりにテニスをした。
kinō, hisashiburi ni tenisu o shita
I played tennis yesterday for the first time in ages.
ネットで予約して、店に向かった。
netto de yoyaku shite, mise ni mukatta
I booked online and headed to the restaurant.
そろそろ休憩しようか。
sorosoro kyūkei shiyō ka
Shall we take a break soon?
The potential is できる — not される, not せられる
This is the pitfall the whole page is built around. The potential of する is the suppletive verb できる（to be able to）. It is not formed by any regular rule, and it is emphatically not される (that is the passive) or せられる (a stiff, classical causative-passive). English speakers, having just learned that 一段 verbs make the potential in 〜られる, keep trying to build a potential of する the same way — and every attempt is wrong.
私は運転できない。
watashi wa unten dekinai
I can't drive.
この漢字、読み方が説明できますか。
kono kanji, yomikata ga setsumei dekimasu ka
Can you explain how to read this kanji?
Because できる is itself a full 一段 verb, it conjugates normally: できる・できます・できない・できた・できて・できれば. In noun + する compounds, the noun simply attaches to できる: 予約できる ("can reserve"), 運転できる ("can drive"), 説明できる ("can explain"). See できる: the suppletive potential for the deep dive. (A literary "can" also exists in 〜し得る（しうる／しえる）, seen in formal writing, but できる is the everyday form.)
Passive される and causative させる
The passive される and the causative させる both live on the さ stem, and they carry their full range of meanings — including the "adversative" passive (something done to your detriment) and the causative's make/let split.
会議は来週に延期された。
kaigi wa raishū ni enki sareta
The meeting was postponed to next week. (passive)
部長は私に残業させた。
buchō wa watashi ni zangyō saseta
The department head made me work overtime. (causative)
Stack the passive onto the causative and you get the causative-passive させられる ("be made to do"), one of the most common ways to complain about work:
部長に無理やり残業させられた。
buchō ni muriyari zangyō saserareta
The department head forced me to work overtime. (causative-passive — done unwillingly)
The imperative splits: spoken しろ vs written せよ
する has two imperatives, and the split is by register, not meaning.
- しろ — the ordinary spoken command. Blunt, forceful, masculine; used for orders, anger, coaching, emergencies.
- せよ — the written/formal imperative. It survives in exam instructions, mathematical problems, military commands, slogans, and set literary phrases. Saying せよ out loud in conversation sounds archaic or theatrical.
ぐずぐずしないで、早くしろ！
guzuguzu shinaide, hayaku shiro!
Stop dawdling and hurry up! (spoken, harsh)
次の問いに答え、理由を説明せよ。
tsugi no toi ni kotae, riyū o setsumei seyo
Answer the following question and explain your reasoning. (written exam instruction)
You will see せよ constantly on test papers and in formal written directives — 注意せよ ("take note"), 準備せよ ("prepare") — but you would never issue those as spoken orders in せよ form.
Every noun + する verb conjugates right here
The payoff for memorizing this paradigm is enormous: Japanese turns nouns into verbs wholesale by adding する, and all of them inflect on this same する. 勉強（study）→ 勉強する; 電話（phone）→ 電話する; 予約（reservation）→ 予約する; 結婚（marriage）→ 結婚する. Every form you learned above transfers directly.
毎晩、二時間ぐらい日本語を勉強している。
maiban, nijikan gurai nihongo o benkyō shite iru
I study Japanese for about two hours every night.
着いたら電話してね。
tsuitara denwa shite ne
Call me when you get there, okay?
So 勉強する gives 勉強します・勉強しない・勉強して・勉強した・勉強できる・勉強される・勉強させる・勉強しよう・勉強すれば・勉強しろ — the whole table, prefixed. See する compound verbs for the details, including when the whole compound takes を directly (日本語を勉強する) versus splitting the noun off with の (日本語の勉強をする).
Common mistakes
❌ 私は料理されない。
Wrong (intending 'I can't cook') — される is the passive ('gets cooked'), not the potential. To say 'I can't cook,' use できる: 料理できない.
✅ 私は料理できない。
watashi wa ryōri dekinai
I can't cook.
❌ 会議のあと、残業せられた。
Wrong — せられる is the old classical causative-passive. Modern Japanese uses させられる.
✅ 会議のあと、残業させられた。
kaigi no ato, zangyō saserareta
After the meeting, I was made to work overtime.
❌ 今日は何もさない。
Wrong — the negative stem is し, not さ. する→しない, never ×さない.
✅ 今日は何もしない。
kyō wa nani mo shinai
I'm not doing anything today.
❌ 急いでいるなら、早くせよ。
Register error (said to a friend) — せよ is the written imperative and sounds archaic in speech. Say しろ (or, more gently, 早くして) to a friend.
✅ 急いでいるなら、早くしろ。
isoide iru nara, hayaku shiro
If you're in a hurry, get moving.
Key takeaways
- する is irregular and memorized whole; its stem shifts し／せ／す／さ across forms.
- Core forms: する・します・しない・した・して・できる・される・させる・しよう・すれば・しろ／せよ.
- The potential is the suppletive できる — never ×される (passive) or ×せられる (classical). Say "can do" with できる.
- The imperative splits by register: spoken しろ, written/formal せよ.
- Every noun + する verb conjugates on this same する, so this one table unlocks thousands of verbs.
Now practice Japanese
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Japanese→Related Topics
- 来る: Full Irregular ParadigmN5 — The complete paradigm of 来る (kuru, to come) — the second of Japanese's two irregular verbs — where the kanji 来 never changes but its reading shifts こ／き／く across the forms, so 来ない is konai, 来ます is kimasu, and the imperative is the irregular 来い (koi).
- 〜する Compound Verbs: ConjugationN4 — In noun + する verbs like 勉強する and 予約する, only する conjugates — the noun never changes — so the whole する paradigm attaches wholesale, the potential is 〜できる, and older ずる forms shift to じる.
- できる: The Suppletive Potential of するN4 — できる is a regular 一段 verb that serves as the suppletive potential of する — 'can do' — and also means 'be completed / come into being'; the potential of する is never ×される or ×せられる.
- All Forms, All Classes: Master ChartN4 — The one-sheet everything reference — every major verb form (dictionary through causative-passive, volitional, conditional, imperative) down the side and 書く・食べる・する・来る across the top, so you can verify any form without hunting across pages.
- Model Verbs by Class: IndexN5 — The one-stop lookup hub for the Regular Paradigms subgroup — a master table anchoring each verb ending to exactly one worked model verb (会う・書く・泳ぐ・話す・待つ・死ぬ・遊ぶ・読む・取る・食べる・する・来る), its class, and its te-form, with a link to each full paradigm page.