Questions & Answers about Собака защищает свой дом.
Why is собака in the nominative case?
Because собака is the subject of the sentence (“the one doing the action”). In Russian, subjects are in the nominative case.
Why is дом in the accusative case and why is there no preposition before it?
Дом is the direct object (what is being protected), so it takes the accusative case. In Russian, most transitive verbs (like защищает) govern a bare accusative for inanimate things—no preposition is needed.
Why doesn’t Russian use an article (like “a” or “the”) before собака or дом?
Russian simply has no articles. Definiteness or indefiniteness is implied by context, word order, or other words, not by separate “a”/“the” words.
Why do we use свой here instead of ее or его?
Свой is a reflexive possessive pronoun that refers back to the subject of the clause. Since the dog (subject) owns the house (object), you use свой to mean “its own.” If you used ее or его, it would mean “someone else’s” (e.g. “her” or “his,” referring to a different person).
Also, свой must agree with дом in gender (masculine), number (singular) and case (accusative), so it appears as свой here.