Ah, common knowledge, the citation exception that makes all who are citation-phobes raise their fists in triumph. What is common knowledge and, more importantly, what is this rule so cut and dry as, “If it’s common knowledge we don’t have to cite it.”
What does the APA Manual, 6th Edition say about this? It is suspiciously quiet, and I wonder if not citing common knowledge is common knowledge. However, its affiliated website gives us some hints.
Common knowledge, simply defined, is knowledge that everyone knows (or should know). So, for example, when you write in your paper The United States’ rule of law is the Constitution, then you do not necessarily have to cite it: In theory, every American has been taught that the U.S.A’s body of law is the Constitution. Many people abroad even know this fact, too.
Apparently, the common knowledge about common knowledge is that if a fact is seen 5 or more times in different places and sources, then it is common knowledge. Be wary, though! First, the APA does not necessarily confirm this statement. Second, this web wanderer has researched enough information to know that people copy and paste facts (ahem–plagiarize!) from an original webpage that is hastily written and poorly cited. So what you may think is common knowledge may in fact be people copying someone else’s poor habits. In this case, check and confirm facts as much as possible!
There are, of course exceptions!
Setting and context: The APA’s blog explains this exception very nicely in the theme of Thanksgiving, a traditionally North American holiday. “Facts that are common knowledge in one setting may need to be backed up by citations in another. Common knowledge is not an opinion (‘Tamales are better than turkey’) but a fact (‘Thanksgiving is always on Thursday’).(The APA Style Radio Theatre, 2013)” I mentioned above that many people overseas know about the U.S. Constitution–but what about places where it is not known at all? You may wish to cite in that case, because if this fact is not part of the education system, and your superiors are not aware of it, then they may be suspicious and want to confirm it. Your best bet is to understand your audience. If they are international lawyers, for example, the U.S.’ rule of law is probably common knowledge. If it is a foreign high school with a local curriculum, it may not be.
If something is a direct quote: If you are copying from someone else’s work, then you should still cite it because you are lifting directly from his work.
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