A tertiary source is an index or textual consolidation of primary and secondary sources. Some tertiary sources are not to be cited in academic research, rather they should be used as an aid to find other sources.
Overlap with secondary sources
Depending on the topic of research, a scholar may use a bibliography, dictionary, or encyclopedia as either a tertiary or a secondary source. This causes some difficulty in defining many sources as either one type or the other.
In the United Nations International Scientific Information System (UNISIST) model, a secondary source is a bibliography, whereas a tertiary source is a synthesis of primary sources.
Types of tertiary sources
As tertiary sources, encyclopedias, textbooks, and compendia attempt to summarize, collect, and consolidate the source materials into an overview, but may also present subjective, or biased commentary and analysis (which are characteristics of secondary sources).
Indexes, bibliographies, concordances, and databases may not provide much textual information, but as aggregates of primary and secondary sources, they are often considered tertiary sources. So although tertiary sources are both primary and secondary, they are more towards a secondary source because of commentary and bias.
Survey or overview articles are usually tertiary, though review articles in peer-reviewed academic journals are secondary (not be confused with film, book, etc. reviews, which are primary-source opinions).
Some sources that are usually primary sources, such as user guides and manuals, are secondary or tertiary (depending on the nature of the material) when written by third parties.
- Primary, secondary and tertiary sources. Archived 2013-07-03 at the Wayback Machine". University Libraries, University of Maryland. Retrieve 07/26/2013
- "Tertiary Information Sources". Old Dominion University -- ODU Libraries. September 2012. Retrieved 20 June 2013.
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- "Primary, Secondary, and Tertiary Resources". University of New Haven.
- Søndergaard, T. F.; Andersen, J.; Hjørland, B. (2003). "Documents and the communication of scientific and scholarly information: Revising and updating the UNISIST model". Journal of Documentation. 59 (3): 278. doi:10.1108/00220410310472509.