What does "get + object + -ing" mean? Is "let" or "make" inappropriate here?
To "get someone to do something" means to cause someone to do something, often by persuasion. So, the sentence "get humans living on other planets" means to cause human beings to live on other planets. There is the idea that the action is a bit difficult to do. "Let" has the feeling of allowing/giving someone permission to do something, so it is not appropriate here. "Make" has the feeling of force, which is too strong of an action as well. Thus, "get" is most appropriate for expressing this sentence. Ex: Can you get Mom to agree to let us have a sleepover? (Feeling of persuasion) Ex: See if you can get Stacey to do us a favor. (Feeling of persuasion) Ex: It's hard to get Dad to laugh. (Difficult action to achieve)