In academic writing, “common knowledge” refers to information that the average educated reader would accept without needing a source citation to back it up.

There are two main categories of common knowledge:

• Information that most people know
• Information shared by a specific group of people, such as a national or cultural group, or academics in a particular field of study

In academic writing, it’s normally essential to cite your sources, but statements that are considered common knowledge do not need a citation.

Examples of common knowledge

Examples of common knowledge include:

• Information that appears across many sources without a clear origin, such as famous historical dates
• Long-established facts or theories that are foundational to a field, like fundamental equations in physics

It does not include:

• Data and statistics gathered in empirical studies. These should always be cited.
• Interpretations or arguments. If a statement could be reasonably disputed, provide a citation.

The examples below show how subtle the distinction can be:

• Statements about APA Style citation
• Statements about the Amazon rainforest

APA is a common citation style used by students.
This is an undisputed and easily verified fact. It is common knowledge.

APA Style is mainly used in the social sciences, business, and nursing.
For a reader familiar with research, this is likely to be accepted as common knowledge. For a more general readership, you might need to cite it.

APA Style is used in more than 90,000 papers per year.
This is not an undisputed fact and should be attributed to one or more sources.

Do I need a citation?

Common knowledge does not need to be cited in your paper, because it is widely known, undisputed, easily verified, and generally not attributable to a specific author.

To avoid plagiarism, it can be tempting to include a citation for every sentence, but in some cases over-citation can weaken your academic writing. If you are unsure whether or not a statement counts as common knowledge, ask yourself the questions below.

Who is my reader, and what can I assume they know?

Are you writing for a general audience or for experts in the field?

In academic writing, it’s more likely that your reader will be an expert, and you can assume a certain level of shared knowledge. But if you include information from a different field, you should cite it.

Could my reader dispute this statement?

If your reader might be surprised by your statement, question its accuracy, or contest it with other data, it isn’t common knowledge, and you should provide a citation.

If it’s a foundational fact that everyone in the field agrees on, it’s probably common knowledge.

Can my reader easily verify this statement across multiple sources?

If you google it, can you easily find more than five scholarly sources that give the same information without citation? If so, it’s probably common knowledge.

If some of the search results contradict each other or you have to dig further to find the facts, you should provide a citation.

Frequently asked questions about plagiarism

Do I have to cite common knowledge?

Common knowledge does not need to be cited. However, you should be extra careful when deciding what counts as common knowledge.

Common knowledge encompasses information that the average educated reader would accept as true without needing the extra validation of a source or citation.

Common knowledge should be widely known, undisputed and easily verified. When in doubt, always cite your sources.

How can I summarize a source without plagiarizing?

To avoid plagiarism when summarizing an article or other source, follow these two rules:

• Write the summary entirely in your own words by paraphrasing the author’s ideas.
• Cite the source with an in-text citation and a full reference so your reader can easily find the original text.

Can plagiarism be accidental?

Accidental plagiarism is one of the most common examples of plagiarism. Perhaps you forgot to cite a source, or paraphrased something a bit too closely. Maybe you can’t remember where you got an idea from, and aren’t totally sure if it’s original or not.

These all count as plagiarism, even though you didn’t do it on purpose. When in doubt, make sure you’re citing your sources. Also consider running your work through a plagiarism checker tool prior to submission, which work by using advanced database software to scan for matches between your text and existing texts.

 

How is plagiarism detected?

Plagiarism can be detected by your professor or readers if the tone, formatting, or style of your text is different in different parts of your paper, or if they’re familiar with the plagiarized source.

Many universities also use plagiarism detection software like Turnitin’s, which compares your text to a large database of other sources, flagging any similarities that come up.

It can be easier than you think to commit plagiarism by accident. Consider using a plagiarism checker prior to submitting your paper to ensure you haven’t missed any citations.