する
する
suru
Conjugation
= to do
| Form | Japanese | Romaji | Meaning |
|---|---|---|---|
| Dictionary form The plain form you find in a dictionary |
する する |
suru | to do |
| Masu form Polite present / future |
します します |
shimasu | do (polite) |
| Te form Connects clauses, makes requests |
して して |
shite | doing / and do |
| Ta form Plain past |
した した |
shita | did |
| Nai form Plain negative |
しない しない |
shinai | don’t do |
| Masen form Polite negative |
しません しません |
shimasen | don’t do (polite) |
| Nakatta form Plain past negative |
しなかった しなかった |
shinakatta | didn’t do |
| Potential form Can / be able to |
できる できる |
dekiru | can do |
| Volitional form Let’s / I think I’ll |
しよう しよう |
shiyou | let’s do |
Suru (する) is one of only two irregular verbs in Japanese, and it attaches to thousands of nouns to build new verbs on the spot, such as benkyou suru (to study) or souji suru (to clean).
Suru is irregular because it does not follow either the godan (u-verb) or ichidan (ru-verb) conjugation patterns that cover almost every other Japanese verb. Once you learn that its stem is shi, most forms become predictable: shimasu, shite, shita, shinai, and shiyou all just attach the normal endings to that stem. The potential is the most disruptive break: instead of a predictable stem change, the potential of suru is dekiru, a separate word with its own conjugation as an ichidan verb, and there is no way to derive dekiru from suru by rule; it has to be memorized as a pair. Other forms shift stems too, but more predictably: the passive sareru and causative saseru both build on a sa stem, so suru actually spreads across a small set of stems depending on what attaches to it, with dekiru sitting completely outside that system.
Reach for shimasu and shimasen in polite conversation, emails, or with people you don’t know well; drop to suru and shinai among friends and family. Shite is the connector form, used to link actions in sequence or before requests like shite kudasai. Shita and shinakatta report what did or didn’t happen in plain speech. Dekiru stands apart from this pattern entirely and answers a different question: not what someone did, but what they are able to do. Shiyou proposes an action, close to English ‘let’s.’ The pattern that gives suru its extra role is that it attaches directly after a huge number of nouns to turn them into verbs: benkyou suru (to study), souji suru (to clean), renshuu suru (to practice). The noun itself never changes; only suru conjugates, so benkyou shimasu, benkyou shita, and benkyou dekiru all keep benkyou exactly as it is.
Everyday use
今日は宿題をした。
Kyou wa shukudai o shita.
I did my homework today.
Casual / Social Media
さあ、運動しよう!
Saa, undou shiyou!
Alright, let’s work out!
Formal / Cultural context
日本語で説明できますか。
Nihongo de setsumei dekimasu ka.
Are you able to explain it in Japanese?
One mistake is trying to build the potential form by rule, the way you would for a godan or ichidan verb, and guessing something like sareru. Sareru is a real word, but it’s the passive form of suru (‘to be done to’), not the potential, so mixing the two up changes the meaning of the sentence. Dekiru itself conjugates as a normal ichidan verb — dekimasu, dekita, dekinai — completely independent of suru‘s own forms, so once you have dekiru you conjugate that word directly rather than trying to adjust suru. Finally, with noun+suru verbs, learners sometimes try to conjugate the noun itself instead of suru, producing errors like benkyoumasu instead of the correct benkyou shimasu; the noun never changes, only suru does.