Breakdown of Ему не надо волноваться, врач знает своё дело.
не
not
он
he / it (for a masculine noun) / it (for a neuter noun)
врач
doctor
знать
to know
Questions & Answers about Ему не надо волноваться, врач знает своё дело.
Why do we use the imperfective verb волноваться after не надо?
In Russian, negative obligations like не надо (it is not necessary / one shouldn't) almost always require an imperfective infinitive. Even if you are talking about not worrying in this one specific situation, you still use the imperfective волноваться rather than its perfective counterpart.
Why does the sentence start with Ему instead of Он?
Words like надо and нужно are impersonal. In Russian, you don't say "He needs," but rather "To him it is necessary." Therefore, the person who needs (or doesn't need) to do something must be in the dative case, which changes он into ему.
Why does it say своё дело instead of его дело?
Свой (and its neuter form своё) is a reflexive possessive pronoun that means "one's own." You must use it when the owner is the subject of the sentence. Here, the doctor (врач) is the subject, and he knows his own job, so we use своё. If you used его дело, it would mean the doctor knows some other man's job!
What case is своё дело in here?
It is in the accusative case because it is the direct object of the verb знает (knows). Since дело is an inanimate neuter noun, its accusative form looks exactly the same as its nominative (dictionary) form.