свой: the reflexive possessive
свой always points back at the subject of its own clause. Он лю́бит свою́ жену́ is his own wife; Он лю́бит его́ жену́ is somebody else's.
Свой means 'one's own' and it refers back to the subject of the clause it stands in. Он люби́т свою́ жену́ — he loves his own wife. Она́ люби́т своего́ му́жа — she loves her own husband. Мы сде́лали свою́ рабо́ту — we did our own work. Они́ поговори́ли со свои́ми детьми́. It declines exactly like мой: свой, своего́, своему́, свой or своего́, свои́м, о своём; своя́, свое́й, свою́, свое́й, о свое́й; своё, своего́, своему́, своё, свои́м, о своём; свои́, свои́х, свои́м, свои́ми, о свои́х.
The contrast that makes the word necessary is one English cannot draw. Он люби́т его́ жену́ means he loves somebody else's wife; его́ here is a third party, not the subject. Он люби́т свою́ жену́ means he loves his own. The same distinction runs through Она́ взяла́ её су́мку — she took another woman's bag — versus Она́ взяла́ свою́ су́мку, she took her own. Russian expresses the difference grammatically; English has to add the word 'own'. This is not a redundant rule but a real gain in precision.
Two limits on its use. First, the nominative singular masculine свой is effectively not used: in an ordinary sentence you say мой, твой, наш or ваш in the subject slot, and свой appears only in the oblique cases or in the plural. It survives in fixed sayings — Своя́ руба́ха бли́же к те́лу, Ка́ждый хва́лит свой това́р — where the possessor really is the subject of a general truth. Second, свой always belongs to the subject of its own clause, so in a complex sentence it can change who owns what. Он попроси́л, что́бы я верну́л его́ кни́гу means he asked me to return his book; swap in свою́ and the book becomes mine, because the subject of that clause is я.
With the first and second persons, свой and мой or твой are interchangeable, and the difference is one of emphasis rather than correctness. Я взял свою́ кни́гу and Я взял мою́ кни́гу both mean 'I took my book', but the first is the natural choice and the second sounds pointed, as though somebody had suggested the book was not yours. The rule of thumb: use свой whenever the possessor is the subject of the clause, and use мой, твой, наш, ваш, его́, её or их whenever it is not.
Examples
- Он лю́бит свою́ жену́. He loves his own wife. Listen in Russian: Slow in Russian: Он лю́бит свою́ жену́.
- Он лю́бит его́ жену́. He loves somebody else's wife. — его́ points away from the subject Listen in Russian: Slow in Russian: Он лю́бит его́ жену́.
- Она́ взяла́ свою́ су́мку и вы́шла. She took her own bag and went out. Listen in Russian: Slow in Russian: Она́ взяла́ свою́ су́мку и вы́шла.
- Мы сде́лали свою́ рабо́ту сами́. We did our own work ourselves. Listen in Russian: Slow in Russian: Мы сде́лали свою́ рабо́ту сами́.
- Ка́ждый ду́мает о своём бу́дущем. Everyone thinks about their own future. Listen in Russian: Slow in Russian: Ка́ждый ду́мает о своём бу́дущем.
- Я взял свою́ кни́гу, а не твою́. I took my own book, not yours. Listen in Russian: Slow in Russian: Я взял свою́ кни́гу, а не твою́.