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Evaluating Information Sources

Use the information on this guide to help you understand and evaluate the different types of information sources.

Primary, Secondary, or Tertiary?

Distinguishing between primary, secondary, and tertiary sources can be difficult because an item may be considered a primary source in one context but secondary in another. Time is the defining element.


Primary Sources are original materials on which other research is based. They allow researchers to get as close as possible to original ideas, events, or original research from a particular time time period. Primary resources have not been interpreted or evaluated.

Secondary Sources analyze, review, or summarize information found in primary sources or even other secondary sources. These accounts are typically written after the fact and with the benefit of hindsight. Secondary sources provide commentary on or discussion of evidence.

Tertiary Sources consist of information which is a distillation and collection of primary and secondary sources. Encyclopedias are typically considered a tertiary source unless, for example, a researcher is studying how encyclopedias from a particular time period.

Primary, Secondary, & Tertiary Sources