Most researchers and authors within the various science disciplines agree on what constitutes a primary source in their fields. However, distinguishing between secondary and tertiary sources is more problematic and can be widely disputed among researchers, authors, and science librarians.
In the discipline of Library and Information Science, tertiary sources are those items that provide guides to primary and secondary sources such as a bibliography of bibliographies.
Disagreement about secondary versus tertiary sources in the sciences seems to originate from determining whether the source of information goes through one or two levels of distillation. Secondary sources derive their information from primary sources (one distillation), whereas authors who support a more extensive list of tertiary sources state that tertiary sources derive their information from either primary or secondary sources. The latter would then require two distillations prior to publication. Since both categories use information originally published in primary sources, the distinction between secondary and tertiary sources becomes somewhat moot, nor does this distinction impact their usefulness as information sources.
Students may wish to check with specific course instructors regarding which option they use.
Examples of sources identified by the proponents of tertiary sources: