When is the preposition ON used? Or, "when do we use the preposition ON". To keep it simple, with time, for example "I work on Mondays" or place "It's on the table". to go abroad on A trip to learn on courses In your example sentences I see these as places where the trip or course takes place. You can be on a course or on a trip. I think it's best to read a lot and get used to how prepositions are used.