You Do Not Have to Document

“Common Knowledge”

Common knowledge is information that is generally known and, therefore, need not be cited as the idea of one particular author.  If you read the same information in three or more general sources, you can assume it is common knowledge.  However, any facts or data found in general sources still need to be cited in your paper, and the reference source listed in your bibliography.  –  New Century Handbook

You need not document “common knowledge.”  This term refers to information that is generally known or accepted by educated people.  Information that you can find readily in general reference works such as encyclopedias or in the popular media is probably common knowledge and need not be documented.  But common knowledge should be verified.  Be certain that several sources provide the same information before assuming that it is common knowledge.  Well-proven historical facts and dates need not be documented.  As a general rule, it is better to over-document than to under-document and be accused of plagiarism.  When in doubt, document.  –  New Century Handbook

What do you not have to document?  When you write a paper that draws on outside sources, you are not expected to document common knowledge or your own thinking.  Common knowledge is information that most educated people know, although they might need to remind themselves of certain facts by looking information up in a reference book.  –  Quick Access Reference for Writers

The only exception is common knowledge – information that your readers could find in any number of general sources because it is commonly known.  For example, the current population of the United States is common knowledge in such fields as sociology and economics.  Freud’s theory of the unconscious is common knowledge in the field of psychology.

As a rule, when you have seen certain information repeatedly in your reading, you don’t need to document it.  However, when information has appeared in only one or two sources or when it is controversial, you should document it.  If a topic is new to you and you are not sure what is considered common knowledge or what is a matter of controversy, ask someone with expertise.  When in doubt, cite the source. –  A Writer’s Reference