Questions & Answers about Мой брат отказался пить вино из принципа.
Why do we use из here instead of от for 'out of'?
This is the core difference between these two prepositions of cause. We use из + Genitive for a conscious, deliberate motive, like a personal principle, curiosity, or politeness. We use от + Genitive for involuntary physical or emotional reactions, like shaking from fear or crying from pain. Since acting on principle is a conscious choice, из is the correct word.
Why is the imperfective verb пить used after the perfective отказался?
In Russian, verbs meaning 'to refuse', 'to stop', or 'to finish' almost always take an imperfective infinitive. Because the brother refused to drink, the action of drinking is completely cancelled and won't happen at all. The imperfective is used to simply name the action that is being avoided.
What case is принципа?
It is in the Genitive case. Both of the cause prepositions из and от always require the noun that follows to take the Genitive case. The dictionary form (Nominative) of this word is принцип.
Could I say отказал instead of отказался?
No, because they mean different things. The reflexive verb отказаться (with the -ся ending) means 'to refuse' to do something yourself or 'to decline' an offer. The non-reflexive отказать means 'to deny' someone else a request. Since the brother is refusing to perform the action himself, the reflexive ending is required.