Breakdown of Он кладёт кошелёк в свой карман.
он
he / it (for a masculine noun) / it (for a neuter noun)
в
in / to (direction)
класть
to put, lay (flat)
свой
one's own
Questions & Answers about Он кладёт кошелёк в свой карман.
Why do we use свой here instead of его for "his"?
The word свой means "one's own" and always refers back to the subject of the sentence, which is Он (He). If we said в его карман, it would mean he is putting the wallet into someone else's pocket!
Why doesn't the ending of свой change here if it is the object of a preposition?
It actually is in the Accusative case! Because the word it describes, карман (pocket), is a masculine inanimate noun, its Accusative form looks exactly the same as its Nominative form. So свой stays свой.
Doesn't the preposition в usually mean "in" and take the Prepositional case?
It takes the Prepositional case to describe a static location (where something is), but it takes the Accusative case for direction or motion (where something is going). Since he is putting the wallet into the pocket as a destination, we use the Accusative case here.
What verb does кладёт come from? The spelling looks very different from regular verbs.
It comes from the infinitive класть (to put). This is an irregular verb where the stem changes in the present tense by adding a д. It conjugates as я кладу, ты кладёшь, он кладёт, and so on.
Is the word кошелёк also in the Accusative case?