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 can I explain to people that the phrase off of is grammatically incorrect? I've heard this phrase used a lot, especially by Americans (though they aren't the only ones). In my understanding, off of should usually be replaced by off, as in, I took the book off the shelf as opposed to I took the book off of the shelf Am I wrong? Or is there perhaps some simple way I can explain this to most people?.

I don't know how you can explain to people in general that it's grammatically incorrect, but here is one idea: when you go to a James Brown tribute concert and the singer says 'Get up offa that thing' what you could do is to trounce the security guards, climb on to the stage, pounce onto the singer, grab the microphone and say 'In fact you should be saying not 'get up offa that thing' but 'get up off that thing' since 'offa' is grammatically incorrect.' I'm sure everyone will thank you for your grammatical corrections. Being serious for a moment though, it's very difficult to decide what is or is not 'grammatically correct'. E.g. in the UK we say 'outside my house' but US people often say 'outside of my house'. How can you actually decide which of these two is grammatically correct? Unfortunately it's not possible since English grammar is not a science like physics but merely a description of what people actually do, and that has changed very significantly over the years. If I was teaching someone English I would definitely say 'off' is correct and 'off of' is wrong, but this kind of decision is based on intuition, based on the usages of educated native speakers.