基本助詞 · Core case markers
で
Means / action location
Marks the means or instrument of an action, the location where an action happens, or the cause/reason in some patterns.
When to use
- Means: バスで行く (go by bus)
- Action location: レストランで食べる
- Material: 木で作る
- Cause in 病気で休む
How to use
- 1Attach で after the noun indicating means or place of action.
- 2Contrast with に: で for dynamic action at/in a place; に for static existence or direction endpoint.
- 3Ranges of time can use で: 一時間で終わる.
Cautions
Nuance & non-standard uses
Patterns that go beyond the textbook default — contrast, omission, register shifts, and mixed particles.
で as cause or reason (病気で・事故で)
When で follows a noun describing a circumstance, it can mean "because of / due to" — overlapping with から but often more objective or factual. Common in news and explanations.
台風で電車が止まった。
Trains stopped due to the typhoon.
不注意でミスした。
Made a mistake through carelessness.
では / じゃ — topic + location or context
では attaches a place or situation as the frame for the rest: 日本では, ここでは. In conversation じゃ is the casual form. This is not "action location" で alone — it is で + thematic は.
うちではあまり食べない。
At our house we don't eat much of it.
それじゃ困る。
That won't work (in that case) — じゃ from では.
で for material / composition
Material or ingredients use で: 木でできている, 小麦粉で作る. English "made of/from" maps here, not に.
この家は木でできている。
This house is made of wood.
Time span で (一時間で・三日で)
で after a duration can mean "within / in (that amount of time)" for completion: 三時間で終わった. Do not use に for this sense — it is a common transfer error from English "in three hours."
二日で直した。
Fixed it in two days — span needed to finish.
Examples
箸で食べる。
Eat with chopsticks.
図書館で勉強する。
Study at the library.