Here's my attempt: I think of "on fire" as an idiom meaning that the house has caught fire, and at least some part of it is burning. "In fire" would mean completely emerged in flames. Anton EDIT: Also see:
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
GuyperHow do I exactly know when to use "on" instead of "in"to describe a state on an object or vice versa?By reading and listening to English as much as possible and remembering which preposition is used in each case. Write these expressions down and drill yourself on them until they become very familiar to you. Many choices of preposition are simply tradi