Most feminine nouns ending in a soft sign (-ь) follow standard third-declension rules. However, two of the most important family words in Russian—мать (mother) and дочь (daughter)—are irregular.
The Hidden "-ер-" Stem
Whenever these two nouns change case (except in the Accusative singular, which matches the Nominative), their stem expands by adding -ер-.
| Case | Singular | Plural |
|---|
| Nominative | мать, дочь | матери, дочери |
| Accusative | мать, дочь | матерей, дочерей |
| Genitive | матери, дочери | матерей, дочерей |
| Dative | матери, дочери | матерям, дочерям |
| Instrumental | матерью, дочерью | матерями, дочерьми |
| Prepositional | матери, дочери | матерях, дочерях |
Note: Like regular third-declension nouns, the Genitive, Dative, and Prepositional singular all end in -и, while the Instrumental singular ends in -ью. Because these are animate nouns, their Accusative plural matches the Genitive plural.
Singular Forms in Context
Let's look at how these expanded stems work in the singular, introducing extended family vocabulary like отчим (stepfather) and мачеха (stepmother).
The verb заботиться (to care) takes о + Prepositional case, and гордиться (to be proud) takes the Instrumental case.
Plurals and Relationships
In the plural, the -ер- stem remains, and most endings follow standard soft-stem rules (like -ям, -ях). You will often use these forms when discussing отношения (relationships) across generations.
