Irregular Verbs: する / くる (Group 3)
Japanese has just two truly irregular verbs: する (to do) and くる (to come). Their conjugations don't follow the vowel rules and must be memorized.
Structure
する and くる — memorize each form individually.
Examples
する → します / しない / した / して
Suru → shimasu / shinai / shita / shite
Do: polite / negative / past / te-form
The core vowel changes (su → shi) across forms.
来る(くる) → 来ます(きます) / 来ない(こない)
Kuru → kimasu / konai
Come: polite / negative
The kanji 来 stays the same, but its reading changes: く → き → こ.
勉強する → 勉強します / 勉強しない / 勉強した
Benkyou suru → benkyou shimasu / benkyou shinai / benkyou shita
Study: polite / negative / plain past
Noun + する compounds conjugate exactly like する itself (su → shi).
• The Power of する: attach する to a Chinese-origin or abstract noun to verbify it — 勉強 (study) + する = to study; 買い物 (shopping) + する = to shop. • Survival Tip: since there are thousands of "noun + する" verbs, mastering する conjugation instantly unlocks a huge portion of the dictionary.
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones Irregular is tested against.
vs Regular う/る-verbs
Group 1 and 2 verbs follow predictable vowel/stem rules; する and くる do not — their stem vowels change irregularly (し/す, き/く/こ) and must be memorized.
More verb forms
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