Use 'in' with periods of time:
in January
in 1978
in the twenties
in the 20th century
in Spring
in the morning / afternoon / evening BUT we say 'at night'
Use 'in' a period of time in the future to express that an action will occur after that amount of time:
in a few weeks
in a couple of days
On
Use 'on' with days of the week:
on Monday
on Fridays
Use 'on' with specific calendar days:
on Christmas day
on October 22nd
At
Use 'at' with an exact time:
at six o'clock
at 10.30
at two p.m.
at noon
at midnight
at night
And now, click on the icon below to take a 15-question preposition quiz
