Masculine nouns in -ок, -ец, -ень and -ёк
Masculine nouns with no ending (they end in a consonant) are where vowels most often disappear. Once any ending is added, in any case or the plural, the vowel goes. Four word endings make it very likely.
| Case | оте́ц · father | день · day | пода́рок · present |
|---|---|---|---|
| Nominative | оте́ц | день | пода́рок |
| Genitive | отца́ | дня | пода́рка |
| Dative | отцу́ | дню | пода́рку |
| Accusative | отца́ | день | пода́рок |
| Instrumental | отцо́м | днём | пода́рком |
| Prepositional | об отце́ | о дне | о пода́рке |
| Nominative plural | отцы́ | дни | пода́рки |
Only the nominative singular (and the accusative of things, which matches it) keeps the vowel. A few feminine nouns in -ь also lose it: любо́вь → любви́ (love), це́рковь → це́ркви (church).
Same ending, different behaviour
The patterns are strong but not absolute. A vowel only flees if it was not part of the original root. Dictionaries always show the genitive (оте́ц, отца́), and learning the two forms together settles the question.
The genitive plural: о́кон, де́вушек, сестёр
Feminine nouns in -а and neuter nouns in -о have no ending in the genitive plural (the form after “five”, “many”, “there are no”). If that leaves two consonants at the end, a vowel is slipped between them. Which vowel depends on its neighbours.
| Insert | When | Examples |
|---|---|---|
| о | Usually before or after к, г, х, or between hard consonants. | |
| е | After a soft consonant, ж, ш, ч, ц, or before к after them. | |
| ё | When the inserted vowel is stressed after a soft consonant. | |
| ь / й → е | A soft sign or й between consonants becomes е. |
кафе́, метро́, такси́: borrowed words keep their shape
Nouns borrowed from other languages that end in -о, -е, -и, -у or -ю are indeclinable: they have one form for every case and for the plural. Adjectives and verbs around them still change, so you need to know their gender.
| Gender rule | Words | Example |
|---|---|---|
| Neuterthe default for things | кафе́, метро́, кино́, пальто́, меню́, такси́, ра́дио, интервью́ | |
| Masculineby tradition | ко́фе | |
| By sexwords for people | атташе́, ле́ди, ма́дам, конферансье́ | |
| Masculineanimals | кенгуру́, шимпанзе́, по́ни | |
| Gender of the categoryplaces, by the word го́род, река́ | Со́чи, То́кио, Миссиси́пи |
Also indeclinable: surnames in -ко, -ых and -аго (Шевче́нко, Седы́х), foreign women’s names ending in a consonant (Ка́рмен), and most abbreviations read as letters (МГУ). Borrowed words ending in a consonant, like компью́тер and парк, change normally.