Given the task definition and input, reply with output. 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.

How should often be pronounced in formal speech? 'off-ten' or 'of-fen'?.

'Should' is inappropriate in the question. Both pronunciations occur. In the 19th century /:fn/ ('aufn') was the normal pronunciation, so in The Pirates of Penzance, there is an elaborate joke on the confusion of 'often' and 'orphan'.