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Primary, Secondary, Tertiary Sources: Guide


This research guide contains information about primary, secondary, and tertiary sources. If you get stuck, please ask a librarian!

Primary sources offer firsthand evidence. In the humanities, this might be letters, diaries, or creative works. In the sciences, the article that first reports the results of an experiment or trial is considered a primary source.  

Secondary sources are one step removed from the primary source. They analyze or interpret past events, creative works, or research findings.

Tertiary sources are "sources about sources" - several steps removed from the primary source. Their focus is on presenting information that is widely agreed on. They are sometimes published with no named author. Examples are general encyclopedias and bibliographies. 

Primary, Secondary and Tertiary Source Definitions

Primary sources online

Primary sources in the TLU library

Library Catalog

You can find primary sources in the TLU Library by searching the library catalog. Use Advanced Search to combine your search term with the subject heading Sources (use the drop-down menu to select Subject). 

Reader's Guide to Periodical Literature

The library has an index called the Reader's Guide to Periodical Literature. It is a physical reference source located on the main floor. You can use it to find articles by subject in the library's bound periodicals such as:

  • Time (starting in 1927)
  • Harper's Monthly Magazine (starting in 1902)
  • The Atlantic (starting in 1981)
  • Good Housekeeping (starting in 1930)

You can also use the Reader's Guide to locate periodical articles that the library does not own and request them through ILL. 

Opinion Archives

Provides full-text access (including backfiles) to American Spectator (1967-present)Commentary (1945-present)Commonweal (1924-present)Dissent (1954-present)Harper's (1850-present)La Follette's Magazine (1909-1929), Moment (1975-present)The Nation (1865-present)National Review (1955-present)The New Leader (1924-present)The New Republic (1914-present)The New Yorker (1925-present)Orion (1982-present)The Progressive (1909-present)The Washington Monthly (1969-present), and The Weekly Standard (1995-present).

American Antiquarian Society Historical Periodicals Collection

Provides full text for 6863 unique titles published between 1684 and 1912. Provides rich content detailing American history and culture from the Colonial Era through the Civil War and Reconstruction. This database covers advertising, health, women's issues, science, the history of slavery, industry and professions, religious issues, culture and the arts, and more. Link to the collection

Guide Editor

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Taylor Gardner
Summer 2021 Practicum Student

Ask a Librarian

Reference desk

TLU librarians offer in-depth research help.

Chat or Text

Ask a Question: The system will prompt you to send a text or an email, or a live chat if a librarian is available. 


During library open hours, ask at the main desk for help finding what you need or help setting up an appointment with a librarian. 






--Interlibrary Loan--

Need an item that our library doesn't own? No worries, you can email the title, author and date of what you need to or fill out a form. We can get most (but not all) articles within 2 days and many books within 4-8 days. 

For more information, visit our interlibrary loan page.