What makes a source primary?

Depends on the topic; it can be complicated.  Talk specifics with your advisor.

Very basic, simplistic definition: What is a primary source?

Useful Tips

Browse footnotes and bibliographies of books, encyclopedias, and articles for information about primary sources. >/p> Search the Library Catalog for primary sources-- modern editions in print and online, sometimes in translation, of original primarysources. Use the advanced search with your topic words in combination with the term sources. In the context of a library catalog, sources means primary sources, either primary sources themselves in modern editions, or books about primary sources, or excerpts of primary sources.

Collections of Classical Texts Online

Hathi Trust Digital Library

Better than Google Books!

Cornell's membership in the Hathi Trust Digital Library allows searching full text of recent copyrighted materials as well as older public domain works. Very useful!