に

に after a place marks where a movement ends: "to". The place comes first, then に, then a verb of movement such as going, coming or going back.

へ marks a destination too, and with these verbs you can use either.

Where something is

With あります and います, に marks the place where a thing or a person is: "in", "at", "on".

に or で

に is the place where something is or ends up. で is the place where an action is done. Eating, reading, buying and studying are actions, so their place takes で.

• × 図書館に勉強します → 図書館で勉強します

A point in time

A clock time, a day of the week or a date takes に: "at", "on".

Words that place a time relative to now take nothing: きょう, あした, きのう, いま今. Nor does まいにち毎日. With a day of the week に may be left out.

• × あしたに行きます → あした行きます

Usage notes

These go beyond a place and a time.

The person on the receiving end

に marks the person an action is aimed at – the one you give to, write to, ask or phone.

With もらいます (to receive), the same に marks the person it came from.

Verbs that take に where English has no "to"

A few everyday verbs take に for what English treats as a plain object: the person you meet, the vehicle you get on, the place you go into.

• × 友達を会います → 友達に会います
• × 電車を乗ります → 電車に乗ります

Going somewhere to do something

Take ます off a verb, add に and a verb of going or coming: "go to do".

A noun that names an activity takes に directly.

Becoming

With なります (to become), に marks what something turns into. A な-adjective takes に here as well.