•[+ to infinitive] If you have not signed a contract, you are under no obligation to (= it is not necessary to) pay them any money.如果你没有签合同，你就没有义务付给他们钱。

•You have a legal obligation to (= The law says you must) ensure your child receives a proper education.法律规定你有义务确保自己的孩子接受合理的教育。

•I haven't got time to do his work for him - I've got too many obligations as it is.我没有时间帮他干活儿——我自己的事还多得做不完呢。