Paraphrasing Plagiarism

Once you cite the source, you have credited the original author, and some textual similarity is acceptable. However, citation does not give you permission to copy structure or language extensively. A good paraphrase should be substantially rewritten—different vocabulary, different sentence structure, rearranged logic. A citation means 'this idea comes from here,' but does not mean 'this wording comes from here.' If you are reusing phrases or sentence patterns substantially, consider using quotation marks around those phrases in addition to citation, or rewrite more thoroughly.

There is no fixed similarity threshold. A proper paraphrase should be written as if you are explaining the idea to someone unfamiliar with the original. Change vocabulary (use synonyms and different terms), restructure sentences, reorganize the logical flow, and add your own commentary or interpretation. If a reader could lay your paraphrase next to the original and see the same words in the same order, it is too close. A good test: can you explain the paraphrased idea from memory, or are you copying while changing words? If the latter, either quote and cite, or study the material more thoroughly and then write.

Common knowledge in a field is often cited anyway for credibility and to direct readers to foundational sources. When in doubt, cite. However, widely known facts that are not attributed to a specific source in the original literature (e.g., 'photosynthesis is the process by which plants convert sunlight to chemical energy') do not require citation. If you can find multiple independent sources making the same claim, it is likely common knowledge. If an idea is traced to a specific researcher or publication, it is not common knowledge and must be cited regardless of how well-known it is in the field.

Cite the secondary source (the one you actually read). Do not cite the primary source unless you have read it directly. If you want to cite the primary source, you must read it. Alternatively, you can note in your text that the idea comes from primary source X 'as cited in' secondary source Y. This is honest attribution and protects you from misrepresenting what you have read. Never cite a source you have not read; this is a form of plagiarism and creates false attribution trails.