Hi I would say that an obligation applies where you have promised a person or you have a contract: - The boss said I must work on Sunday but I never agreed to that: I have no obligation Duty usually applies in a social situation: - We take turns to clean the fridge at work: I didn't want to do it last Friday, but it was my duty My own view is that moral imperatives are usually in the verb ... - He was very rude: he must apologise - He killed a man: he should go to prison - She stole from the local shop: you just don't do that We do say: - He's only paying her $7 an hour? That's immoral!
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