When do you need to reference?

• When you are using or referring to somebody else's words or ideas from a magazine, book, newspaper, song, TV program, movie, Web page, computer program, letter, advertisement, or any other medium.
• When you use information gained through interviewing another person.
• When you copy the exact words or a "unique phrase" from somewhere.
• When you reprint any diagrams, illustrations, charts, and pictures.
• When you use ideas that others have given you in conversations or over email.

• When you are writing your own experiences; your own observations, such as your own experimental results; your own insights; your own thoughts; your own conclusions about a subject.
• When you are using "common knowledge" - folklore, common sense observations, shared information within your field of study or cultural group.

What is considered "common knowledge" depends on the audience you are writing for. Example: If referring to a well-known Māori legend in an assignment for a Māori Studies course, a reference may not be necessary. But if referring to the same legend in an assignment for a Psychology course or in a paper for an international journal, a reference would be needed.

Material is probably common knowledge if

• You have found the same information undocumented in at least five other sources.
• You expect your readers to already know about this information.
• The information could be easily found in a general reference source.
• The information is considered as a generally accepted fact.

Source: Owl Writing Lab, Purdue University