By now, you know that most singular nouns take the ending -е in the Prepositional case. However, there is a special group of nouns that take the ending -ии instead.
If a noun ends in -ия, -ие, or -ий in its dictionary (Nominative) form, its Prepositional singular ending will always be -ии. Notice that you simply replace the final letter (я, е, or й) with и.
| Gender | Nominative Ending | Prepositional Ending | Example |
|---|
| Feminine | -ия | -ии | химия ➔ о химии |
| Masculine | -ий | -ии | планетарий ➔ в планетарии |
| Neuter | -ие | -ии | предприятие ➔ на предприятии |
Let's see how this rule applies across academic fields, laboratories, and specialized institutions.
Feminine nouns ending in -ия
Feminine nouns ending in -ия (like лаборатория, химия, академия, астрономия) change their ending to -ии. This pattern is extremely common with academic subjects and institutions.
Masculine nouns ending in -ий
Masculine nouns ending in -ий (like планетарий, санаторий, сценарий) also take the -ии ending in the Prepositional case.
Neuter nouns ending in -ие
Finally, neuter nouns ending in -ие (like предприятие, заседание, отделение) complete the pattern, taking the exact same -ии ending.
