When to Cite
Ohio State University Libraries Teaching & Learning and Robyn Hartman
Citing sources is often portrayed as a straightforward, rule-based practice. However, the reality is more complex, with many gray areas around citations. Mastering citation guidelines is a skill that takes practice and education.
If you find it confusing, rest assured that you are not alone – in fact, your confusion may indicate that you are engaging in critical thinking. Here are some guidelines to help you navigate the intricacies of citation practices:
- Cite when you are directly quoting.
- Cite when you are summarizing and paraphrasing.
- Cite when you are citing something that is highly debatable.
- Don’t cite when what you are saying is your own insight.
- Don’t cite when you are stating common knowledge.
Cite when you are directly quoting.
This is the easiest rule to understand. If you are stating word-for-word what someone else has already written, you must put quotes around those words, and you must give credit to the original author. Not doing so would mean that you are letting your reader believe these words are your own and represent your own effort.
Cite when you are summarizing and paraphrasing.
This is a trickier area to understand. Summarizing and paraphrasing are two related practices, but they are not the same. Summarizing is when you read a text, consider the main points, and provide a shorter version of what you learned. Paraphrasing is when you restate what the original author said in your own words and in your own tone. Both summarizing and paraphrasing require good writing skills and an accurate understanding of the material you are trying to convey. Summarizing and paraphrasing are difficult to do when you are a beginning academic researcher, but these skills become easier to perform over time with practice.
Cite when you are citing something that is highly debatable.
For example, if you want to claim that the Patriot Act has been an important tool for national security, you should be prepared to give examples of how it has helped and how experts have claimed that it has helped. Many U.S. citizens concerned that it violates privacy rights won’t agree with you, and they will be able to find commentary that the Patriot Act has been more harmful to the nation than helpful. You need to be prepared to show such skeptics that you have experts on your side, too.
Tip: This section covers how and when to cite sources. For a discussion of why to cite sources, see Ethical Use of Sources.
Don’t cite when what you are saying is your own insight.
Research involves forming opinions and insights around what you learn. You may be citing several sources that have helped you learn, but at some point, you must integrate your own opinion, conclusion, or insight into the work. The fact that you are not citing it helps the reader understand that this portion of the work is your unique contribution developed through your own research efforts.
Don’t cite when you are stating common knowledge.
What is common knowledge is sometimes difficult to discern. Quick facts like historical dates or events are generally not cited because they are common knowledge. Common knowledge refers to widely known and accepted information, not the result of individual research or interpretation.
Examples of information that would not need to be cited include:
- The Declaration of Independence was signed in 1776.
- Barack Obama became the 44th president of the United States in January 2009.
Some quick facts, such as statistics, are trickier. For example, the number of gun-related deaths per year probably should be cited because there are a lot of ways this number could be determined (does the number include murder only, or suicides and accidents, as well?). There might be different numbers provided by different organizations, each with an agenda about gun laws.
A guideline for deciding whether to cite facts is to determine whether the same data is repeated in multiple sources. If it is not, it is best to cite.
The other thing that might make this determination difficult is that what seems new and insightful to you might be common knowledge to an expert in the field. You have to use your best judgment and probably err on the side of over-citing as you learn to do academic research. You can seek the advice of your instructor, a writing tutor, or a librarian. Knowing what is and is not common knowledge is a practiced skill that gets easier with time and with your own increased knowledge.
Ask three questions to determine common knowledge:
- Is this fact widely known by educated people?
- Can I find it in numerous general reference sources?
- Am I using someone else’s exact words, ideas, analysis, data, or statistics?
If the answer to #3 is yes, cite it. If the answer to #1 and #2 is yes and the information is a basic fact, it is usually common knowledge and does not require a citation.
Common Knowledge Examples
|
What |
Common Knowledge |
Citable Information |
Why |
| Historical Facts | The United States declared independence from Great Britain in 1776. | According to historian Gordon Wood, the American Revolution fundamentally transformed social relationships and political authority in the colonies. | The date of independence is widely known and easily found in many sources. A historian’s interpretation or analysis is someone else’s scholarly contribution and requires citation. |
| Science | Water boils at 100°C at sea level. | A 2024 study found that a new desalination technology reduced energy consumption by 30% compared to previous methods. | Basic scientific facts are common knowledge; specific research findings must be cited. |
| Literature | Shakespeare wrote Romeo and Juliet. | Smith argues that Juliet displays greater agency than Romeo throughout the play. | The authorship of the play is common knowledge. Scholarly interpretations belong to specific researchers and need citation. |
| Psychology | Stress can affect a person’s mental and physical health. | Research by Jones and colleagues found that college students who practiced mindfulness for eight weeks reported significantly lower stress levels. | General concepts may be common knowledge, but specific studies and results always require citation. |
| Business | Amazon is one of the world’s largest online retailers. | Amazon held approximately 38% of the U.S. e-commerce market in 2025. | Market-share statistics are specific data that must be traceable to a source. |
| Health | Regular exercise is generally associated with better health. | The American Heart Association recommends at least 150 minutes of moderate-intensity aerobic activity per week. | Specific recommendations from an organization require citation. |
| Economics | Inflation refers to a general increase in prices over time. | The U.S. inflation rate was 3.2% in a particular year. | Definitions may be common knowledge, but numerical statistics require citation. |
Why You Can’t Cite Wikipedia
You’ve likely been told at some point that you can’t cite Wikipedia, or any encyclopedia, in your scholarly work.
The reason is that such entries are background resources meant to prepare you to do research, not evidence of your doing it. Wikipedia entries, which are tertiary sources, are already a summary of what is known about the topic. Someone else has already done the labor of synthesizing lots of information into a concise and quick way of learning about the topic.
So, while Wikipedia is a great shortcut for getting context, background, and a quick lesson on topics that might not be familiar to you, don’t quote, paraphrase, or summarize from it. Just use it to educate yourself.
Activity: To Cite or Not to Cite?
Chapter Attribution:
Choosing and Using Sources: A Guide to Academic Research by Teaching & Learning, Ohio State University Libraries, licensed under CC BY 4.0
Information taken word-for-word from another source and either spoken by you or incorporated into your written work. Quoting someone else directly is acceptable in most cases, sometimes even required. But you should always name the person you are quoting and the source where you found the direct quote.
One of the techniques you can use to integrate material from a source into your research paper. Summarizing what a source says lets you make another author’s long text piece shorter for your reader, yet still retains the author’s meaning. Your summaries require citations to give credit and avoid plagiarism.
In your own work, using the ideas of others by putting them in your own words. This is a way of using your sources when their ideas and meaning is more important than the exact language the author used and when you don’t need to use the author’s preeminent authority to bolster your argument at the moment. Paraphrases require in-text and bibliographic citations of the sources whose ideas you are using.
Information widely known and accepted, which typically does not require citation.
Sources that provide general, factual, or historical context for a topic.
Sources that provide third-hand information. That is, they are not the original or primary source (say, a novel) and are not second-hand information (such as a book review of that novel), which is always about the original source and usually by someone other than the creator of the original source. Instead, tertiary sources abstract, compile, digest, or otherwise organize primary and secondary sources. Examples are dictionaries, encyclopedias, guides, and handbooks. Tertiary sources are those you usually wouldn’t read from beginning to end.
Combining ideas and perspectives to create a new way of thinking about something. Synthesis is generally thought of as the opposite of analysis, although analysis is often necessary in order to synthesize. Synthesis is different from summarization because summarization makes a shorter, concise version of something that exists, while synthesis makes something new.
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