Tertiary source


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 some academic disciplines the differentiation between a secondary and tertiary source is relative.
In the United Nations International Scientific Information System 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.
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.
Almanacs, travel guides, field guides, and timelines are also examples of tertiary sources.
Survey or overview articles are usually tertiary, though review articles in peer-reviewed academic journals are secondary.
Some sources that are usually primary sources, such as user guides and manuals, are secondary or tertiary when written by third parties.