直す vs 治す: To Fix vs To Heal — The Transitive なおす Pair Explained

In a previous article we explored 直る (naoru) and 治る (naoru) — the intransitive verbs that mean “something gets fixed” or “something heals on its own.” Now it’s time for the other side of the same coin: 直す (naosu) and 治す (naosu), the transitive pair where someone actively does the fixing or healing. Both are read the same way, but they’re written with different kanji and used in completely different situations.

There’s also a bonus: 直す has a powerful secondary function as a compound verb suffix — think やり直す (to redo), 書き直す (to rewrite), and 言い直す (to rephrase). This makes it one of the most frequently used verb structures in everyday Japanese. By the end of this guide, you’ll know exactly which verb to use, when the two can overlap, and how to build compound verbs naturally with 直す.

直す (naosu) — To Fix, Repair, or Correct Something

直す is the transitive counterpart of 直る. Whereas 直る means “something gets fixed by itself,” 直す means you (or someone) actively fixes it. The kanji 直 carries the sense of straightening, setting right, or restoring to a correct state. The object being fixed takes the particle を.

The range of 直す is broad: you can use it for physical repairs, text corrections, behavioral changes, and more. Think of anything you actively put back into its correct or intended state.

Repairing physical objects

• パソコンを直す。— To fix the computer.
• 自転車のタイヤを直した。— I repaired the bicycle tire.
• 壊れた時計を直してもらった。— I had my broken watch fixed.
• 屋根の雨漏りを直すのに業者を呼んだ。— I called a contractor to fix the roof leak.
• ドアの鍵が壊れたので直した。— The door lock was broken, so I fixed it.

Correcting mistakes, text, or documents

• 文章の間違いを直す。— To correct the mistakes in the text.
• レポートをもう一度直してから提出してください。— Please fix your report once more before submitting it.
• 翻訳の誤りを直した。— I corrected the errors in the translation.
• 先生が私の作文を直してくれた。— The teacher corrected my essay.
• 誤字を直すのに時間がかかった。— It took time to fix the typos.

Reforming habits, posture, or behavior

• 悪い癖を直すように努力している。— I’m making an effort to break my bad habit.
• 姿勢を直しなさい。— Fix your posture.
• 遅刻する癖を直したい。— I want to break the habit of being late.
• 話し方を直すために練習している。— I’m practicing to improve my way of speaking.
• 子供のうちに生活習慣を直すべきだ。— You should fix your lifestyle habits while you’re young.

Formation note: 直す is a Group 1 verb (五段動詞). Its て-form is 直して and its past form is 直した.

治す (naosu) — To Cure, Heal, or Treat an Illness or Injury

治す is the transitive counterpart of 治る. Where 治る means “an illness heals on its own,” 治す means a person, doctor, or medicine actively works to eliminate the illness or injury. The kanji 治 is always connected to the body, health, and medicine. The thing being treated takes the particle を.

A key cultural note: Japanese speakers often say things like 早く風邪を治してね (Get well soon — literally “cure your cold quickly”) even though we know colds heal on their own. The speaker is encouraging active effort toward recovery.

Treating illness

• 早く風邪を治してね。— Get well soon (lit. cure your cold quickly).
• 医者が病気を治した。— The doctor cured the illness.
• この薬が感染症を治すのに効果的です。— This medicine is effective at treating the infection.
• 難しい病気を治す新しい療法が開発された。— A new therapy to cure a difficult illness was developed.
• 漢方薬でアレルギーを治そうとしている。— I’m trying to cure my allergy with Chinese herbal medicine.

Healing injuries

• 怪我を治すためにリハビリをしている。— I’m doing rehabilitation to heal my injury.
• 医者が骨折を治すために手術した。— The doctor performed surgery to fix the fracture.
• 自分で傷を治そうとしている。— I’m trying to heal the wound myself.
• 背中の痛みを治すにはどうすればいい？— How should I go about healing my back pain?
• 捻挫を治すのにどのくらいかかりますか？— How long does it take to heal a sprain?

Formation note: 治す is also a Group 1 verb. Its て-form is 治して and its past form is 治した. Notice that 直して and 治して are written the same way in romaji — the kanji is the only distinction in writing.

The Overlap: 癖を直す vs 癖を治す

One area where 直す and 治す can both appear is with 癖 (くせ, habit) and behaviors seen as harmful or unwanted. Learners often wonder: which one is correct?

In practice, 直す is far more commonly used for habits and behaviors. 治す tends to be reserved for habits that feel more like physical or psychological conditions (e.g., nail-biting, thumb-sucking, a nervous tic). When in doubt, 直す is the safer choice for everyday habits.

• 悪い姿勢を直すために毎日ストレッチしている。— I stretch every day to fix my bad posture.
• 夜更かしの癖を直したい。— I want to break the habit of staying up late.
• 爪を噛む癖を治すのが難しい。— It’s hard to cure the habit of biting my nails. (治す = treating like a condition)

一直す as a Compound Verb: やり直す, 書き直す, and More

One of the most important things to know about 直す is that it functions as a verb suffix meaning “to do [verb] again” or “to redo [verb] properly.” This compound verb pattern (Verb-stem + 直す) is extremely common in everyday Japanese and appears across all proficiency levels.

To form this pattern, take the verb stem (the ます-form without ます) and attach 直す directly. The meaning becomes “to do X again” or “to X over correctly.”

Example sentences with compound 直す

• もう一度やり直しましょう。— Let’s do it over.
• レポートを最初から書き直した。— I rewrote the report from scratch.
• その箇所をもう一度読み直してみてください。— Please try reading that part again.
• 失礼なことを言ってしまったので、言い直した。— I said something rude, so I rephrased it.
• このプロジェクト、根本から考え直す必要がある。— We need to rethink this project from the ground up.
• 間違えてしまったので、データを入力し直した。— I made a mistake, so I re-entered the data.
• フォームに記入ミスがあったので、書き直してください。— There was an error in the form, so please fill it out again.

Notice that 〜直す carries a sense of correcting something that went wrong or taking a second attempt at something. This nuance is slightly stronger than simply “doing X again” (for which 〜もう一度〜する is more neutral).

Side-by-Side: When to Use 直す vs 治す

Transitive vs Intransitive: The Full なおす/なおる Picture

To keep the full なおす/なおる family straight, here is the complete reference. The key question is always: Does someone actively cause the change, or does it happen naturally?

DECISION GUIDE
─────────────────────────────────────────────────────
Are you (or someone) actively doing the fixing or healing?
  YES ─► Transitive (naosu)
          ├─ Physical object / text / habit / behavior → 直す
          └─ Illness / injury / body → 治す

  NO ─► Intransitive (naoru) — it happens naturally
          ├─ Physical object / habit → 直る
          └─ Illness / injury → 治る

BONUS: Verb-stem + 直す = "do [verb] again/properly" (e.g. やり直す)
─────────────────────────────────────────────────────

Natural Conversations

Yuka

このレポート、間違いが多いね。もう一度直してもいい？ — There are a lot of mistakes in this report. Can you fix it again?

Rei

ごめん、すぐに書き直します。 — Sorry, I’ll rewrite it right away.

Yuka

やり直すの大変じゃない？ — Isn’t it hard to redo it?

Rei

でも正確さが大事だから。ちゃんと直したいです。 — But accuracy is important, so I want to fix it properly.

Yuka

車、まだ直ってないの？ — Is the car still not fixed?

Rei

うん、修理店に持って行って直してもらうよ。— Yeah, I’ll take it to the repair shop and have them fix it.

Yuka

風邪、ひどそうだね。早く治してね。— Your cold looks bad. Get well soon.

Rei

ありがとう。今日は薬を飲んで早く寝る。— Thanks. I’ll take some medicine and go to bed early today.

Yuka

怪我を治すのにどのくらいかかりそう？— How long do you think it will take for your injury to heal?

Rei

先生には二週間って言われた。リハビリも頑張る。— The doctor said two weeks. I’ll work hard at rehab too.

Common Mistakes English Speakers Make

Using 直す for illness

❌ 風邪を直す。

✅ 風邪を治す。

The kanji 直 is associated with straightening objects or correcting text — not healing the body. Any time the subject is an illness or injury, use 治す.

Using 治す for repairing objects

❌ パソコンを治す。

✅ パソコンを直す。

The kanji 治 is always medical or health-related. Machines, text, and behavioral habits all use 直す.

Forgetting the compound verb usage

❌ もう一度やります。(neutral — just “I’ll do it again”)

✅ やり直します。(implies correcting or redoing properly after a mistake)

When you want to convey “I’m redoing this to fix it,” using the compound 〜直す is more precise and natural than もう一度〜する.

Confusing the は/を particles

❌ 病気は治す。(unnatural — は makes 病気 the topic, not the direct object)

✅ 病気を治す。(を marks 病気 as the thing being actively cured)

Both 直す and 治す require を to mark what is being fixed or cured. は can appear for contrast, but を is the standard particle here.

Quick Quiz

Fill in the blank with the correct verb: 直す or 治す.

• この文章の誤字を______ください。(Please fix the typos in this text.)
• 医者は難しい病気を______ことができる。(Doctors can cure difficult illnesses.)
• 提案書をもう一度______必要がある。(The proposal needs to be rewritten — use the compound form.)
• 骨折を______ためには安静が大切だ。(Rest is important to heal a broken bone.)
• 話し方の癖を______のは難しい。(It’s hard to break speaking habits.)
• システムのエラーを______のに一日かかった。(It took a day to fix the system error.)

Answers: 1. 直して  2. 治す  3. 書き直す  4. 治す  5. 直す  6. 直す

Ready to use these verbs in real conversation? italki connects you with native Japanese tutors for one-on-one practice — the fastest way to make 直す, 治す, and their compound forms feel natural.