What needs a citation
Cite a source whenever you use someone else's work. That includes:
- Exact words, in quotation marks.
- Ideas or arguments you put in your own words (paraphrases and summaries).
- Facts, statistics and data that are not common knowledge.
- Images, charts, tables and other media.
Common knowledge, such as facts most readers would know or could find in many general sources without dispute, usually doesn't need a citation. The line can be fuzzy. When in doubt, cite.
Quoting, paraphrasing and summarizing
A paraphrase that keeps the original sentence and swaps a few words for synonyms is still too close to the source, even with a citation. Read the passage, close it, write the idea from memory, then compare to check you haven't copied phrasing.
The main citation styles
Different subjects use different styles. Your teacher or the assignment will tell you which one to use.
| Style | Often used in | In the text | List at the end |
|---|---|---|---|
| MLA | English, literature, languages and other humanities | Author and page number in the text, for example (Last 42) | Works Cited |
| APA | Psychology, education, nursing and many social sciences | Author and year in the text, for example (Last, 2020, p. 42) | References |
| Chicago, notes and bibliography | History and some arts subjects | Numbered footnotes or endnotes | Bibliography |
| Chicago, author-date | Some sciences and social sciences | Author and year in the text | References |
All of these styles use two parts: a short citation in the text where you use the source, and a full entry in a list at the end. The short citation points the reader to the full entry.
What a full entry includes
The order and punctuation differ by style, but most entries need the same pieces of information:
- Author or authors, or the organization if there is no named author.
- Title of the work, and the title of the larger work it appears in, such as a journal or website.
- Publisher or site name.
- Date of publication.
- Page numbers for print sources or articles in journals.
- A DOI or URL for online sources, where the style asks for one.
As a rough pattern, a book in MLA style looks like Last, First. Title of Book. Publisher, Year. and in APA style like Last, F. (Year). Title of book. Publisher. Treat these as shapes only. The exact rules for capitals, italics, edition numbers and online sources are in the official style guide.
Style guides publish new editions every few years and the rules change. Use the edition your course requires. Your school library's citation guide and the official style manuals are the reliable references.
Citation generators
Library databases and many websites will produce a citation for you. They save time but often get details wrong, such as capitals, missing authors or wrong dates. Check every generated citation against the source and the style guide before you hand in your paper.
Habits that make citing easy
- Save citation details the moment you find a source.
- Mark quotes and paraphrases clearly in your notes. See notes that keep sources straight.
- Add in-text citations while you draft, not after.
- Build your list of sources as you go and sort it at the end.
Citation questions
Do I need to cite something I already knew?
If it is common knowledge, no. If you knew it because you read it somewhere specific, and it isn't widely known, cite where it can be found.
Do I cite my own earlier work?
Yes. Reusing your own earlier paper for a new assignment without permission and without citing it is treated as a breach of integrity at many schools. Ask your teacher first. See academic integrity.