Cite Common Knowledge

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You will often hear your instructors say that you do not need to cite any pieces of information which are considered “common knowledge.” Generally, this term is taken to refer to information which the average reader would be familiar with, and thus accept as reliable without having to do much further research. Unfortunately, there will not always be a consensus on who constitutes the average reader, or what information ought to fall under this umbrella. As such, you must always be cautious when deciding whether a familiar piece of information requires citation.

In order to decide whether a piece of information is common, you should first ask yourself a couple of questions, namely:

Who is my audience, and what are their areas of expertise?

Usually, what is considered common knowledge is dependent on the reader. Some pieces of information are used frequently in certain fields and rarely in others. For example, you could reasonably assume that the editors of the scientific journal Nature would be familiar with Newton’s Laws of Universal Gravitation, but you could not necessarily do the same for your peers in a Creative Writing seminar.

Am I likely to be questioned on either the legitimacy, or source of my information?

If you are using a piece of information which seems even remotely contentious, your audience will likely question you on its validity. In which case, you must ensure that they can verify what you have said by providing a citation. The same can be said for information which appears surprising, or confusing.

Is my information discussed frequently in non-academic circles?

If the information that you are referring to would be as familiar to the clerk at your local grocery store as it would be to your professor, it is likely common knowledge. Many facts will be familiar to most members of your community, regardless of their respective levels of education. These facts may be taught in primary school, topical in the news, or basic realities of life; so long as you can expect most people to know them, they are common. Do note, however, that not all information which is widely assumed is also accurate. For instance, while it is commonly held that the sky is blue because it reflects the colours of the ocean, this is not, in fact, true.

What about culturally-specific common knowledge?

As discussed above, whose knowledge constitutes common knowledge can vary depending on your situation. If you grew up surrounded by a specific culture or language, you may possess a common knowledge that in understood by people who share those experiences, but not understood by those who don't. This is a good example of when it may be worth reaching out to your instructor or peers about whether your culturally-specific common knowledge is something that they share or are aware of, and whether they think more description is needed. Your instructor especially will be able to give you direction as to whether/how you need to cite it.

Should you ever find yourself in doubt when answering any of these questions, it would be best to simply provide a citation. While you may face serious penalties for failing to cite an important piece of information, you will almost never be penalized for over-citation.

Again, this answer depends on who your audience is. However, any information which is factual, non-controversial, and either widely known to most members of your community, or can easily be verified by them is likely considered common knowledge. For example:

  • John A. Macdonald was the 1st Prime Minister of Canada
  • Quebec is a predominantly French-speaking province located in Eastern Canada
  • The Ming Dynasty ruled over China prior to the Qing Dynasty
  • Haile Selassie I was the last reigning Emperor of Ethiopia
  • 0 degrees Celsius is the temperature at which water begins to freeze

If your work is solely intended for an audience with specialized knowledge on its subject matter, the bounds of what constitutes common knowledge may be considered broader. In such a case, citations for standard principles, laws, or concepts would be redundant, as you could reasonably assume that your audience would understand what you were referring to. For instance:

  • Say’s Law – or the Law of Markets – would be familiar to most economists
  • Archimedes’ Principle of Buoyance would be familiar to most physicists
  • Hegelian Dialectic would be familiar to most philosophers
  • Ohm’s Law of Electricity would be familiar to most engineers
  • Proust’s Law of Definite Composition would be familiar to most chemists

While it is not always easy to determine whether something is common knowledge, some types of information definitively do not fall under this umbrella. In general, if a piece of information is either not yet widely accepted, or refers to highly specific data which you could not reasonably expect your audience to remember, it is not common knowledge. Accordingly, such information requires citation. Examples of this include:

  • Information from datasets constructed by you or others
  • References to specific studies conducted by others
  • References to specific dates or numbers that the reader would not know unless they had conducted similar research
  • Statistics obtained from institutions like Statistics Canada or the United Nations

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