Q: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
For example, a man's name is Jeff Smith. My question is: When should I call him 'Jeff'? When should I call him 'Smith'? When should I call him 'Jeff Smith'? in western.
A:
In general US usage, you would use 'Jeff' if you are friends, contemporaries, or Jeff has asked you to use his first name. First names are often used in casual settings. You would use 'Mr. Smith' (or 'Dr. Smith' or other appropriate title) if you are colleagues, younger than Mr. Smith, or in a formal or business setting. You would use 'Smith' in a very casual setting, particularly when playing sports. You would use 'Jeff Smith' when making an introduction, or if you needed to distinguish him from other Jeffs or Smiths, or sometimes when greeting him.