Prepositional Case

The prepositional (предложный падеж) is the only case that never stands alone. It always follows a preposition, which is exactly where its name comes from. Its two everyday jobs are location (where something is) and the topic of speech or thought (what something is about).

The prepositional is the most regular case of all: almost everything ends in -е. There's one important exception to memorise and one small group of "locative" nouns.

1. Location: with в and на answering где? (where?): в школе, на столе.
2. Topic: with о (about): говорить о книге, думать о будущем.
3. Circumstance: with при (in the presence of / at the time of): при Петре Первом.

The same prepositions в and на take two different cases depending on meaning. Location (где?) → prepositional; direction toward (куда?) → accusative. This pair is worth drilling until it's automatic:

Same preposition, opposite endings: в школе → в школу. With the prepositional done, just the instrumental remains. The cases overview ties all six together.

Putting -е on -ия / -ие nouns. These take -ии: it's на лекции and в здании, never лекцие / здание.

Confusing location with direction. Use the prepositional for being somewhere (я в школе), the accusative for going somewhere (я иду в школу). Leaving a noun in -е when you mean motion is the classic slip.

Using -е for the locative nouns. A handful of masculines take a stressed -у for location: в лесу, not в лесе.