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Primary, secondary, and tertiary sources

When searching for information on a topic, it is important to understand the value of primary, secondary, and tertiary sources.

Primary sources allow researchers to get as close as possible to original ideas, events, and empirical research as possible. Such sources may include creative works, first hand or contemporary accounts of events, and the publication of the results of empirical observations or research. We list sources for historical primary documents.

Secondary sources analyze, review, or summarize information in primary resources or other secondary resources. Even sources presenting facts or descriptions about events are secondary unless they are based on direct participation or observation. Moreover, secondary sources often rely on other secondary sources and standard disciplinary methods to reach results, and they provide the principle sources of analysis about primary sources.

Tertiary sources provide overviews of topics by synthesizing information gathered from other resources. Tertiary resources often provide data in a convenient form or provide information with context by which to interpret it.

The distinctions between primary, secondary, and tertiary sources can be ambiguous. An individual document may be a primary source in one context and a secondary source in another. Encyclopedias are typically considered tertiary sources, but a study of how encyclopedias have changed on the Internet would use them as primary sources. Time is a defining element.

While these definitions are clear, the lines begin to blur in the different discipline areas.

In the humanities and social sciences, primary sources are the direct evidence or first-hand accounts of events without secondary analysis or interpretation. A primary source is a work that was created or written contemporary with the period or subject being studied. Secondary sources analyze or interpret historical events or creative works.

Primary sources

  • Diaries
  • Interviews
  • Letters
  • Original works of art
  • Photographs
  • Speeches
  • Works of literature

A primary source is an original document containing firsthand information about a topic. Different fields of study may use different types of primary sources.

Secondary sources

  • Biographies
  • Dissertations
  • Indexes, abstracts, bibliographies (used to locate a secondary source)
  • Journal articles
  • Monographs

A secondary source contains commentary on or discussion about a primary source. The most important feature of secondary sources is that they offer an interpretation of information gathered from primary sources.

Tertiary sources

  • Dictionaries
  • Encyclopedias
  • Handbooks

A tertiary source presents summaries or condensed versions of materials, usually with references back to the primary and/or secondary sources. They can be a good place to look up facts or get a general overview of a subject, but they rarely contain original material.

Examples

SubjectPrimarySecondaryTertiary
ArtPaintingCritical review of the paintingEncyclopedia article on the artist
HistoryCivil War diaryBook on a Civil War BattleList of battle sites
LiteratureNovel or poemEssay about themes in the workBiography of the author
Political scienceGeneva ConventionArticle about prisoners of warChronology of treaties

In the sciences, primary sources are documents that provide full description of the original research. For example, a primary source would be a journal article where scientists describe their research on the genetics of tobacco plants. A secondary source would be an article commenting or analyzing the scientists' research on tobacco.

Primary sources

  • Conference proceedings
  • Interviews
  • Journals
  • Lab notebooks
  • Patents
  • Preprints
  • Technical reports
  • Theses and dissertations

These are where the results of original research are usually first published in the sciences. This makes them the best source of information on cutting edge topics. However the new ideas presented may not be fully refined or validated yet.

Secondary sources

  • Monographs
  • Reviews
  • Textbooks
  • Treatises

These tend to summarize the existing state of knowledge in a field at the time of publication. Secondary sources are good to find comparisons of different ideas and theories and to see how they may have changed over time.

Tertiary sources

  • Compilations
  • Dictionaries
  • Encyclopedias
  • Handbooks
  • Tables

These types of sources present condensed material, generally with references back to the primary and/or secondary literature. They can be a good place to look up data or to get an overview of a subject, but they rarely contain original material.

Examples

SubjectsPrimarySecondaryTertiary
AgricultureConference paper on tobacco geneticsReview article on the current state of tobacco researchEncyclopedia article on tobacco
ChemistryChemical patentBook on chemical reactionsTable of related reactions
PhysicsEinstein's diaryBiography on EinsteinDictionary of relativity