Although virtually all professional and student writing guides, including those in the sciences, provide specific instructions on the proper use of quotation marks, references, etc., some fail to offer specific details on proper paraphrasing. With some exceptions, writing guides that provide instructions for proper paraphrasing and for avoiding plagiarism tend to subscribe to a "conservative" approach to paraphrasing. That is, these guides often suggest that when paraphrasing, an author must substantially modify the original material. Consider the following examples of paraphrasing guidelines:

Don’t plagiarize. Express your own thoughts in your own words…. Note, too, that simply changing a few words here and there, or changing the order of a few words in a sentence or paragraph, is still plagiarism. Plagiarism is one of the most serious crimes in academia.

You paraphrase appropriately when you represent an idea in your own words more clearly and pointedly than the source does. But readers will think that you plagiarize if they can match your words and phrasing with those of your source.