Wikipedia:Classification of sources

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Wikipedia articles are based on three types of sources: primary, secondary and tertiary. These types (primary sources, secondary sources and tertiary sources) arise from the field of Historiography, but their working definition on Wikipedia is precised from the traditional meaning, as suitable to our purposes of summarizing existing scholarship and complying with Wikipedia:Verifiability, Wikipedia:No original research, and Wikipedia:Neutral point of view.

What is a primary source?

A primary source is a source authored or documented by a person who was in a position to know the cited facts, either through personal observation or through immediate and contemporary contact with a witness. Examples of primary sources are: a photograph, a journal article relating experimental results and conclusions, a diary entry, an interview of an eye-witness recorded in a newspaper, a work of fiction, quotations recorded by a listener, village gossip relating to contemporary events, and observation-based conclusions.

If given in their proper context, primary sources can be a neutral and informative way to present information in a Wikipedia article. Often, however, the import or significance of primary sources is not obvious or is controversial, in which case they must be supported by secondary sources.

What is a secondary source?

A secondary source is any source authored by someone who was not in a position to know the cited facts, usually for the purpose of interpretation, commentary, or argument. Secondary sources rely on primary sources and other secondary sources. Examples of secondary sources are: an analysis of a controversial photograph, a journal article relying on data presented in other journal articles, a work of history drawing on diaries, newspaper clippings, and village gossip, and critical commentary.

Non-controversial and respected secondary sources are often more neutral and informative than primary sources. Sometimes, however, secondary sources act as filters and add "spin" to primary sources. Therefore, polemical or controversial secondary sources must be balanced with other secondary sources, and typically by reference to the unvarnished primary sources, so that the reader can have a basis to determine which secondary source provides the most credible "spin" on the primary sources.

What is a tertiary source?

A tertiary source is a special case of a secondary source that relies on other primary and secondary sources—it is in the nature of an authoritative or comprehensive overview. Examples of tertiary sources are: a textbook, a treatise, an atlas, and a dictionary. Wikipedia is itself a tertiary source.

Well-respected tertiary sources, such as textbooks and legal treatises, can be the most neutral secondary sources for use in Wikipedia articles. Frequently, however, the process by which the author collected the information is unclear and not well documented, and sometimes, the author is unknown. In such cases, tertiary articles should be supported by primary and other secondary sources.

Use-dependent classification

It is not always possible to describe a single source as primary, secondary, or tertiary. The classification depends in part on the use of the source. For example, consider a biography of Alexander the Great written by a Roman in the time of the Roman Empire. As it informs us on the life of Alexander it is a secondary source because the author did not personally know Alexander or witness his doings, but as it informs us on the world-view of Roman society, it is a primary source because the author is in a position to know first-hand the details of typical Roman life.