直す, 治す, 直る, and 治る: matching readings, different domains
Separate 直 for repairing objects or correcting errors from 治 for curing illnesses or healing injuries. Learn the action of fixing something and the change of something recovering together with their particles.
直す and 直る for objects and errors
直す is used to repair a broken object or correct faulty content or a distorted shape. 曲がった眼鏡のフレームを直しました。 marks the bent glasses frame being repaired with を.
直る describes the object returning to a normal state. 修理が終わって、コピー機が直りました。 marks the copier that became usable again with が.
治す and 治る for illness and injury
治す focuses on curing an illness or healing an injury. 早く病気を治すために、医者の指示どおり薬を飲みます。 marks the condition to be cured with を.
治る describes a physical condition recovering. 傷が治るまで、この指を水につけないでください。 marks the healing wound with が. This sentence alone does not identify who treated it.
Choose the spelling from the noun and context
The verbs in パソコンの故障を直す and 風邪を治す are both read なおす. The first corrects a mechanical problem, while the second cures an illness. In writing, check which domain the accompanying noun belongs to.
The verbs in 時計が直りました and けがが治りました are both read なおりました. In speech, nouns such as 時計 and けが reveal the meaning; in writing, 直 and 治 make the distinction visible.
Quick check: How should なおる be written in ノートパソコンがなおりました。 when a repaired laptop starts working again?
Show the answer and why
Write ノートパソコンが直りました。 The situation concerns a mechanical fault being corrected, rather than an illness or injury healing, so use 直る.