直す vs 治す
JLPT N4 vocabulary · what is the difference?
Both are read なおす, so the kanji is the whole distinction: 治す is for bodies — curing an illness, healing an injury — and 直す is for everything else, repairing an object or correcting a mistake. Because they sound identical, this pair only matters when you write.
When to use each
直す
なおす
Write 直す when you repair a thing, correct an error, or put something back the way it should be — a bike, a sentence, a translation, a habit.
自転車を直してもらいました。
じてんしゃをなおしてもらいました。
I had my bicycle fixed.
先生が作文の間違いを直してくれました。
せんせいがさくぶんのまちがいをなおしてくれました。
The teacher corrected the mistakes in my composition.
治す
なおす
Write 治す when what is being restored is a body: an illness, a cold, a wound, a bad tooth. The kanji 治 is the one in 治療, medical treatment.
早く風邪を治してください。
はやくかぜをなおしてください。
Please get over your cold soon.
医者が母の病気を治しました。
いしゃがははのびょうきをなおしました。
The doctor cured my mother's illness.
Sentences where only one works
時計が壊れたので、直します。
とけいがこわれたので、なおします。
The clock broke, so I'll fix it.
An object, so 直す. Writing 治します here would read as though the clock were a patient.
けがを治すのに一か月かかった。
けがをなおすのにいっかげつかかった。
It took a month to heal the injury.
An injury to a body takes 治す, even though English says 'fix up' informally.
この文を正しく直してください。
このぶんをただしくなおしてください。
Please correct this sentence.
Correcting language is always 直す — the sense is 'make it straight', which is what 直 means.
歯を治してもらいに行きます。
はをなおしてもらいにいきます。
I'm going to get my tooth treated.
A tooth is part of the body, so 治す, even though the dentist's work looks like a repair.
Common mistakes
病気を直す
病気を治す
The most common slip, because 直す is learned first and both are typed as なおす. An input method will happily offer 直す; you have to pick 治す for illness.
この間違いを治してください。
この間違いを直してください。
Mistakes are corrected, not cured. The reverse error, and it stands out clearly to a reader.
癖を治す
癖を直す
A habit is normally 直す — you straighten it out. 治す does appear for habits framed as something pathological to be cured, but 直す is the safe and usual choice.
Frequently asked questions
If they sound the same, does it matter when I speak?
No. In speech the listener takes the meaning from the object — 病気を or 自転車を settles it instantly. The distinction is a writing and typing problem only.
What is 治る versus 直る?
The same split, intransitive: 風邪が治る means the cold gets better by itself, 時計が直る means the clock is working again. The transitive and intransitive pairs keep the same kanji rule.
Which kanji for fixing a bad mood or making up with someone?
機嫌を直す (cheer someone up) and 仲直り (making up) both use 直. Anything about putting a state back to normal that is not a medical condition takes 直.