Transparency and accountability are an indispensable part of academic writing. As the Chicago Manual of Style, 16th Edition (2010) puts it: ‘Ethics, copyright laws, and courtesy to readers require authors to identify the sources of direct quotations of paraphrases and of any facts or opinions that are not generally known or easily checked.’ (p. 655)
Any time you base yourself on information from an external source, you must refer to that source. This enables readers to see exactly what your opinion is based on. It also allows them to see which opinions are yours and which are someone else’s. This makes your research verifiable, which in turn makes it a sound basis for other researchers to build on.
In short, you ensure that the distinction between your own information, opinion or thoughts and those from external sources is crystal clear. You can do this by paraphrasing (part of) the source text, that is, summarizing it in your own words, or by quoting the source text, that is, copying it verbatim in the original language and placing it in quotation marks (or using an English translation in quotation marks and including the original quotation in a note). Each and every paraphrase and quotation is followed by a reference to its source. These references may be footnotes or endnotes. For more information, see the citation guidelines included in this manual.
If you fail to properly reference your sources, you open yourself to accusations of plagiarism. Neglecting to properly reference runs counter to the rules of transparency and accountability. It is bad for scholarly debate and stymies academic research.