What is common knowledge?

The basic rule of thumb for citing sources is that whenever you take information or ideas from a source (internet, journal, book, another person – any other source) you need to tell your reader where you got your information. By the time you are in 11th or 12th grade, you understand that you have to cite your sources. Good.

Now the rules change slightly and we introduce the concept of common knowledge. The basic idea is that if you take a fact from one of your sources, and you have seen that information published in many other places, it can be considered common knowledge, and you do not have to cite things that are common knowledge. Examples of things that are common knowledge are: Pearl Harbor was bombed on December 7th, 1941; the ocean has salty water; snow is cold; Dick Cheney is George W. Bush’s Vice President. These are things that most people know. Common knowledge does not have to be cited.

The following categories of information are considered common knowledge, and do not need to be cited:

1. Information that is widely known
2. Information that is found in many sources
3. Your own observations

You should know that applying the common knowledge principle can be complicated. As your academic career advances, you will find yourself in classes that require advanced knowledge. For example, if you take an Ecology course in college, it may be common knowledge between yourself, your fellow students and your instructor that Bob Payne coined the phrase “keystone predator” to describe an essential species in an ecological food chain. What may be common knowledge to Ecologists and students in that class may not be considered common knowledge to the person in the grocery checkout at the Giant. Thus, the standard of common knowledge changes from situation to situation. Bottom line: you have to judge whether a fact/idea is common knowledge based on your audience.