by itself

by itself — phrase

1. happening or operating without anyone having to control, start, or stop it direc

1.片語B1
釋義

happening or operating without anyone having to control, start, or stop it directly — used mainly for machines, devices, and systems that run on their own.

例句

The front door unlocks by itself when you walk up to it with the key fob.

describes a machine function triggered by a condition

The sprinkler system turns on by itself when the soil moisture drops below a certain level.

同義詞
  • automatically

    the more common adverb for this idea; slightly broader in use

  • on its own

    informal equivalent, very common in everyday speech

反義詞

用法筆記

Subject is always a thing (machine, device, system), never a person. For people doing something without help, use 'by oneself' (e.g., 'He fixed it by himself').

常見錯誤

⚠️ 'The computer turned off by itself' vs. 'The computer turned off automatically / on its own' — All three are natural for self-operating machines, so no correction is needed. 'Automatically' is the most formal; 'on its own' is the most informal.

2. with nothing or no one else nearby; without help from anyone or anything else —

2.片語A2
釋義

with nothing or no one else nearby; without help from anyone or anything else — used to describe something that is physically isolated or an action done without assistance.

例句

The old farmhouse stood by itself at the end of a long, dusty road.

describes physical isolation of a building

The children finished their homework by themselves while their father cooked dinner.

同義詞
  • alone

    more common for people; does not change form for subject

  • unaided

    formal; emphasises the lack of assistance

  • on its own

    informal and very common for both things and people

反義詞

用法筆記

For things: describes physical isolation ('a tree standing by itself'). For people and animals: inflects to match the subject — by myself, by yourself, by himself, by herself, by ourselves, by yourselves, by themselves. This is the sense that most commonly takes each reflexive form.

常見錯誤

❌She sat by itself in the corner.
✅She sat by herself in the corner.
💡'by itself' is for things; use the matching reflexive for people.
❌He carried the box by itself.
✅He carried the box by himself.
💡When the subject is a person, the pronoun must agree with the subject, not the object.