They change depending on whether the thing your expressing relation to is inside or outside, which seems ok until you realize how vague that is. For instance, post office takes the "outside" preposition because the postal service was once people riding on horses outside. And "in" the Ukraine has a different preposition than all other countries because the Ukraine is "outside" of Russia.
Completely arbitrary, and sometimes I think the explanations for why this or that has a different preposition is made up half the time.
no subject
They change depending on whether the thing your expressing relation to is inside or outside, which seems ok until you realize how vague that is. For instance, post office takes the "outside" preposition because the postal service was once people riding on horses outside. And "in" the Ukraine has a different preposition than all other countries because the Ukraine is "outside" of Russia.
Completely arbitrary, and sometimes I think the explanations for why this or that has a different preposition is made up half the time.