Primary vs Secondary vs Tertiary

Primary sources contain raw, original, non interpreted, and unevaluated information. For a history paper, a primary source could be a first-hand account of an event as recorded in a tweet or a diary. For a business paper, it could be raw data from the U.S. Census. Or, for a science paper, a primary source could be a peer-reviewed article presenting original research data.

Secondary sources digest, analyze, evaluate, and/or interpret the information drawn from primary sources. These sources tend to be argumentative, with a thesis that the author is trying to demonstrate. They often take the form of scholarly articles or books.

Tertiary sources compile, analyze, and digest secondary sources. They tend to be factual and straightforward. These often take the form of reference books, such as encyclopedias and handbooks. Because they are easy to understand, tertiary sources are very useful for preliminary research as you are brainstorming your research question.