Possessive Pronoun "Свой"

The pronoun свой, depending on its form and meaning, may be translated as my, your, our, its, their, his, her.

masculine feminine neuter plural
Nominative
Genitive
Accusative
Dative
Instrumental
Prepositional
свой
своего
свой, своего*
своему
своим
своём
своя
своей
свою
своей
своей
своей
своё
своего
своё
своему
своим
своём
свои
своих
свои/своих*
своим
своими
своих

*In the masculine and plural accusative the first one is inanimate, the second one is animate.

So we tend to use the pronoun свой rather than the other possessive pronouns, when the subject of a sentence and the possessor are the same person. Let's look at this example:
    - Я люблю свой город. | I love my city.
Я is the subject of the sentence. And the city is mine. So in this case свой would be used more often than мой, although, technically it wouldn't be a mistake if you used мой. It just wouldn't sound as natural. Let's look at another example:
    - Дай мне свой телефон. Мне нужно позвонить. | Give me your phone. I need to call.
We can't see the subject in the sentence, but we know that it is ты, because дай is the imperative, singular. The pesron we're talking to is the possessor of the phone. That's why we use свой. Again, technically using твой wouldn't be a mistake but we tend to use свой instead.
This is how it works for the first person (я, мы) and the second person (ты, вы). However, in the third person we MUST use свой if the subject and the possessor are the same person. Compare:
    (У Джона есть сестра. | John has a sister.)
  • Джон позвонил своей сестре и пригласил её в ресторан. | John called his sister and invited her to a restaurant.
    (У друга Джона есть сестра. | A friend of John's has a sister.)
  • Джон позвонил его сестре и пригласил её в ресторан. | John called his sister and invited her to a restaurant. (Meaning, he called his friend's sister.)
Other examples:
    (У Алексея есть родители. | Alexey has parents.)
  • Алексей позвонил своим родителям. | Alexey called his parents.
    (Алексей работает учителем. У Ромы проблемы в школе. | Alexey works as a teacher. Roma has some problems in school.)
  • Алексей позвонил его родителям. | Alexey called his parents. (Roma's parents)
    (Алексей работает учителем. У Кати проблемы в школе. | Alexey works as a teacher. Katya has some problems in school.)
  • Алексей позвонил её родителям. | Alexey called her parents. (Katya's parents)
    (Алексей работает учителем. У Кати и Ромы проблемы в школе. | Alexey works as a teacher. Katya and Roma have some problems in school.)
  • Алексей позвонил их родителям. | Alexey called their parents. (Roma and Katya's parents)
So in the third person if the subject and the possessor are the same person, you can't use any other possessive pronouns other than свой. However, when talking about subject's relatives or parts of the subject's body, you don't necessarily need to use any possessive pronoun. It sounds even more natural if you don't.
  • Джон позвонил сестре и пригласил её в ресторан. | John called his sister and invited her to a restaurant.
  • Алексей позвонил родителям. | Alexey called his parents.
  • Я сегодня с братом в пойду в теннис играть. | Today I'm going to play tennis with my brother.
  • Почищу зубы и пойду спать. | I'll brush my teeth and go to bed.
  • Сначала помой руки. | First, wash your hands



Click here to learn more about the possessive pronouns.
Click here to learn more about possessive structures.