High School Writing Mistakes

This is part three of a five-part series on writing mistakes.
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Unlike obvious and elementary writing errors like misspellings and poor grammar, what I like to call high school writing mistakes tend to be more subtle.

1) Have you checked each and every one of your facts for accuracy?

2) Have you taken care to differentiate between fact and opinion in your writing?

3) Have you been assiduous about attributing quotes and ideas so as to avoid even the slightest appearance of plagiarism?

These are important questions that we should all ask ourselves about everything we write, no matter what our level of writing experience. Just take the issue of plagiarism as an example--even the innocent misplacing of a couple of quotation marks or the accidental omission of a source can be enough to seriously harm the reputation of even the most established writer.