When these words refer to LOCATION: "on" = "on top of", "on the front surface of" or "traveling for" Ex. 1: "The cat is on the chair." Ex. 2: "I watched the movie on TV." Ex. 3: "He is on a business trip to Mexico." "in" = "inside of" or "attending" Ex. 1: "The dirty dishes are in the dishwasher." Ex. 2: "Mr. Jones is in a meeting right now." "at" = "near", "visiting", or it is used for events / entertainment (indoors or outdoors), or for locations where the purpose is more important than the building Ex. 1: "The horses were at the trough, eating." Ex. 2: "We had dinner at my friend's house." Ex. 3: "John is at the movies right now." Ex. 4: "I saw Mary at the post office." With locations that have a specific purpose, you use "at" when you are talking about the purpose and "inside" when you need to talk about the building itself: Ex. 1: "The children are at school right now." (purpose, i.e., education) Ex. 2: "There was a fire inside the school today." (the building structure) In English, there are always exceptions to the rule. But these are good, general guidelines that should help with many of your problems of usage.

for time,on means the specific day,in refers to a larger spectrum of time and at refers to a smaller time point; for position:in refers to within some place;at refers to a small point; on refers to the above something

~Prepositions of TIME~ at = designate specific times the train is due at 12:15 p.m. on = designate days and dates -my brother is coming on monday -we're having a party on the fourth of july in = for nonspecific times during a day, a month, a season, or a year. -she likes to jog in the morning -it's too cold in winter to run outside -he started the job in 1971 -he's going to quit in august ~Prepositions of PLACE~ at = specific addresses grammar english lives at 55 boretz road in durham on = designate names of streets, avenues, etc. her house is on boretz road in = for the names of land-areas (towns, counties, states, countries, and continents) -she lives in bandung -bandung is in west java -west java is in java ~Prepositions of LOCATION~ IN -(the) bed* -the bedroom -the car -(the) class* -the library* -school* AT -class* -home -the library* -the office -school* -work ON -the bed* -the ceiling -the floor -the horse -the plane -the train * you may sometimes use different prepositions for these locations

perfect answers above :)