Sources for literature study are divided into primary, secondary and tertiary sources.
In the Humanities, these terms have different meanings as in the sciences.
In the humanities primary sources are the object of the research. The non-scholarly publications that were introduced in the previous chapter are primary sources as they are used as source material in research.
Secondary sources are the publications where researchers publish their results: conference procedures, journal articles, edited volumes and monographs.
Tertiary sources synthesize the accepted knowledge of the secondary sources and create general overviews of the knowledge in the field. They compose a synthesis of the scattered and detailed research results.
Handbooks and reference works belong to this catagory.
Library catalogues and bibliographic databases are also considered tertiary sources, because they organize the secondary sources with the purpose to help people to find what they need.