Prepositions Governing the Prepositional Case
The prepositional case is so named because it is is used only with prepositions, and only four prepositions are currently used with this case: в+Prep "in, at", на+Prep "on, at", о(б)+Prep "about", and при+Prep "on (one's person), during". Notice that the first two have two meanings "in, at" and "on, at". This is because the Russian people have discovered away of ridding their language of any preposition meaning "at": they simply use these two prepositioins (and u+Gen) to mean "at". Because the meanings are so similar (as you will soon see), there is never any confusion.
To keep the 'two' meanings distinct in the English-speaking mind, you need only to remember where you are (easy enough if you're under 50). For example, if you are at home and someone says, Саша в школе, then they mean "Sasha is at school". Since the two places are totally different, Russians can use the general meaning of в+Prep. If you are already at school, standing out on the sidewalk, say, then the same sentence will mean "Sasha is inside the school". Clever, huh? And it works every time. Here are some more examples; the 'at' examples are coded in blue. (See the section on case for and explanation of the case endings.)
The Locative (Place) Prepositions The Preposition в+Prep Саша у себя в комнате. Sasha is in her room. Я забыла ключи в машине. I left the keys in the car. Боря сейчас учится в университете. Borya is at college now. Валя работает в больнице. Valya works at the hospital. The Preposition на+Prep Боря спит на диване. Borya is sleeping on the couch. Валя любит ездить на автобусе. Valya likes to take the bus. Васи не было на лекции. Vasya wasn't at the lecture. Я забыла пальто на концерте I left my coat at the concert.
You might have noticed something unusual about the phrases with на+Prep meaning "at". While the phrases with в+Prep meaning "at" refer to an object that people are normally inside when they are 'at' it, на+Prep is usually used with abstract nouns like concert, lecture, class, meeting. The reason has to do with the rule for choosing between в+Prep and на+Prep. The basic principle is this: f
The 'At' Rule for Russian
In expressing "at" in Russian, choose в+Prep if the location is an inanimate object which human beings are normally inside when they are 'at' it; otherwise, chose на+Prep. (If the object of the preposition is animate, y+Gen is used.)
The rule as stated predicts that if the object is on something people are usually on when they are 'at it', e.g. на поле "in the field", на улице "on the street", or if the object of the preposition refers to an abstract concept like concerts, lectures, etc., на+Prep will be used. В+Prep and на+Prep are also used in various time expressions which require special explanation. They are also used with the accusative case when modifying verbs of motion. Just to spice up what might otherwise be a boringly simple system, the Russians tossed in a couple of exceptions.
The preposition о(б)+Prep means "about" and is used pretty much the same as about is used in English. The preposition при+Prep has two common meanings. The first is "on one's person", as in У меня нет ручки при себе "I don't have a pen on me". The other meaning is "in the time of, during the tenure of", as in Всё это случилось при Петре первом "That happened in the time (during the reign of) Peter I." Here are a few more examples.
Other Prepositional Case Prepositions Они говорили только о работе. All they talked about was work. О чём вы думаете? What are you thinking about? При тебе есть деньги? Do you have any money on you? При Сталине было ужасно. During Stalin's time is was horrible.
No other prepositions currently govern the prepositional case. So let's move on to the prepositions governing the last case, the instrumental.