particle
at, by, with (location/means)
1. at, in (location of action)
Marks the location where an action takes place. 学校(がっこう)勉強(べんきょう)する (study at school). Compare with に, which marks location of existence.
I study at the library.
Location of action
I met my friend at school.
Location of action
I played in the park.
Location of action
I work busily at the company every day.
Location of action
While I was waiting for my friend at the station, it suddenly started raining.
Location of action
2. by, with (means/method)
Indicates the means, tool, or method used to do something. バスで()く (go by bus), 日本語(にほんご)(はな)す (speak in Japanese).
Let's go by train.
Means of transportation
Please write in English.
Language as a means
I eat with chopsticks.
Tool/instrument
Please speak in Japanese.
Means (language)
My older brother commutes to work by bicycle every day, but on rainy days he goes by train.
Means of transportation (contrasting two methods)
3. made of (material)
Indicates what something is made from. ()(つく)る (make from wood).
I made it from wood.
Material
I make a box from paper.
Material
This dish is made from rice and vegetables.
Material
Building a house from stone is difficult.
Material
This chair is made of plastic.
Material
4. due to, because of (cause)
Indicates the cause or reason. 病気(びょうき)(やす)む (absent due to illness).
I was absent from school due to a cold.
Cause/reason
The game was canceled due to rain.
Cause/reason
The train was delayed due to an accident.
Cause/reason
I was tired from work, so I went to bed early.
Cause/reason
The power went out due to the typhoon.
Cause/reason
5. in, within (scope/limit)
Sets a boundary or scope. 三人(さんにん)で (among three people), 一時間(いちじかん)で (within an hour).
Three of us did this work.
Scope/limit (number of people)
The two of us will go.
Scope (number of people)
I live alone.
Scope (by oneself)
It will be finished in one hour.
Scope (time limit)
Can I buy it for 1000 yen?
Scope (price limit)
The whole family went on a trip together.
Scope (group)
6. at (age/situation)
Marks the age or circumstance at which something happens. 二十歳(はたち)大学(だいがく)卒業(そつぎょう)した (graduated from university at 20).
十八歳(じゅうはっさい)大学(だいがく)(はい)りました
I entered university at 18.
Age/situation
I started piano at 5 years old.
Age/situation
It's fine as it is now.
Situation/state
When I was young, I thought I could do anything.
Age/situation
At 30, I decided to start a company.
Age/situation

で vs is crucial: で marks where actions happen (図書館(としょかん)勉強(べんきょう)する), while marks where things exist (図書館(としょかん)(ほん)ある) or destinations (図書館(としょかん)()). で is one of the most versatile particles, covering location, means, material, cause, and scope.

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