- You can ‘t learn a language in six weeks.
One can’t learn a language in six weeks.
One is more formal.
- One usually knocks at a door before going into somebody’s house. Somebody’s knocking at the door. (NOT One is kneeking . . .)
One can usually find people who speak English in Sweden.
English is spoken in this shop. (NOT One speaks English. The meaning is not ‘people in general’.)
One has to believe in something.
In the sixteenth century people believed in witches.
(NOT . . . one believed . . . The group could not include the speaker.)
- He talks to one like a teacher. One’s family can be very difficult.
One should always give oneself plenty of time to pack.