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A citation identifies for the reader the original source for an idea, information, or image that is referred to in a work.
From: Lemieux Library, University of Seattle
Are you quoting two or more consecutive words from a source? Then the original source should be cited and the words or phrase placed in quotes.
If an idea or information comes from another source, even if you put it in your own words, you still need to credit the source.
General vs. Unfamiliar Knowledge
You do not need to cite material which is accepted common knowledge. If in doubt whether your information is common knowledge or not, cite it.
We usually think of books and articles. However, if you use material from web sites, films, music, graphs, tables, etc. you'll also need to cite these as well.