What are the differences in nuance among "need to", "have to", and "should? Are those three always interchangeable?
The phrases "need to" and "have to" are similar to one another and are often used interchangeably. "Should," however, cannot be used interchangeably with the other phrases. This is because of the uncertainty of "should." When you have to do something, it means it's required. When you need to do something, it's also required. When you should do something, it means that you have a choice, and it would be better if you did complete it, but it is not necessary. Ex: I really need to write my paper. Ex: We need to get to the airport by 5. Ex: We have to get going. Ex: He has to go to the dentist. Ex: Should I wait out here or come inside with you? Ex: I think we should leave.