My, Our, svoj in Cases

Possessives change like adjectives to match the noun they go with.

• môj: môjho, môjmu, mojom, mojím; f. mojej, moju, mojou; pl. mojich, mojim, mojimi
• tvoj and svoj follow the same pattern: tvojho, svojmu, svojou
• náš / váš: nášho, nášmu, našom, naším (with); f. našej, našu, našou; pl. našich, našim (to), našimi

Svoj means one's own and points back to the subject: Peter umýva svoje auto. (Peter is washing his own car.) Jeho auto would be someone else's car. With ja, ty, my and vy both svoj and môj are correct.

Jeho, jej, ich never change: s jej bratom (with her brother).