A tertiary source is an index and/or textual consolidation of primary and secondary sources. Some tertiary sources should not be used for academic research, unless they can also be used as secondary sources or 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 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 and textbooks attempt to summarize and consolidate the source materials into an overview, but may also present subjective commentary and analysis (which are characteristics of secondary sources).
Index, bibliographies, and databases may not provide much textual information, but as aggregates of primary and secondary sources, they are often considered tertiary sources.
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- 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.