Rhetorical questions carry the purpose of persuasion, which you obviously don't need in a research paper, where everything is based on fact. This usually applies in the case of discursive essays, or narrations. Plus, an audience listening to a research paper will probably only be interested in the information strictly, and will be irritated by rhetorical questions.
A research paper is fact and nothing but the fact. A research paper is just giving information about a topic. However, rhetorical questions are used to persuade the reader to believe or agree with something, mainly in a discursive essay; but in a research paper, you aren't persuading, you are educating.
Rhetorical questions are discouraged in research papers because they can undermine the objective tone, focus on evidence, and reader's expectations. Instead, research papers should prioritize clarity and straightforward presentation of facts. This approach is critical for maintaining the integrity and effectiveness of academic writing.
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