で details
で — where an action happens, and what it is done with
昨日、公園でバーベキューしたんだ。
kinou, kouen de baabekyuu shita n da.
We had a barbecue in the park yesterday. casual
毎日、自転車で通っています。
mainichi, jitensha de kayotte imasu.
I commute by bicycle every day. neutral
Examples
where the action happens — で marks the site an event takes place at
昨日、公園でバーベキューしたんだ。
kinou, kouen de baabekyuu shita n da.
We had a barbecue in the park yesterday. casual
いつも駅前の図書館で勉強しています。
itsumo ekimae no toshokan de benkyou shite imasu.
I always study at the library in front of the station. neutral
means, tool, medium or material — what the action is done with, or what a thing is made of
毎日、自転車で通っています。
mainichi, jitensha de kayotte imasu.
I commute by bicycle every day. neutral
この箸は竹で作られています。
kono hashi wa take de tsukurarete imasu.
These chopsticks are made of bamboo. neutral
お手続きはオンラインでも承っております。
o tetsuzuki wa onrain de mo uketamawatte orimasu.
You can complete the paperwork online as well. formal
the amount it takes, or the group that does it — で closes off a span of time or a sum of money, and names how many people are acting
三人で行こうよ。
sannin de ikou yo.
Let's go, the three of us. casual
この作業は一日で終わります。
kono sagyou wa ichinichi de owarimasu.
This job will be finished in a single day. neutral
この鞄は千円で買えました。
kono kaban wa sen'en de kaemashita.
I got this bag for a thousand yen. neutral
cause — で names the circumstance behind what happened, in a phrase rather than a clause
風邪で会社を休みました。
kaze de kaisha o yasumimashita.
I took the day off work with a cold. neutral
台風で電車が止まってる。
taifuu de densha ga tomatteru.
The trains are stopped because of the typhoon. casual
Formation
{N}でattaches to noun
Notes
(×教室でいます). The exception is an event noun, which is itself
something that happens: 三階で会議があります.
Related patterns
Similar
で packs the cause into a single NOUN and presents it as a given circumstance (風邪で休みました), while から asserts the link and needs a whole clause — which is why a reason only a proposition can carry takes から, 勉強したいから休みました having no noun で could hold.
The verb picks, not the noun — に names where something IS or ends up (東京に住む, 机の上に置く), で where an action is carried out (東京で働く), so the same 東京 takes either depending on what follows it.
The same place noun before the same motion verb reads two ways — 公園を走る traces a route through the park, 公園で走る names it as the site the running happens at; を follows the path, で bounds the venue.
Lookalikes
病気で splits two ways and only the continuation tells you which — the case で hands its noun to a verb as venue, tool or cause (病気で休んだ), the copular で is だ's て-form predicating it of the subject (彼は病気で、来られません), and only that second one expands back to である.