The definition of 'primary source' does differ in the Humanities, Social Sciences, and Natural and Applied Sciences. The UBC Library offer clear definitions of primary and secondary sources.
The Faculty of History at the University of Cambridge offers a virtual classroom that includes, for example, Reading Primary Sources, How to use Historical Sources, and Where do Historical Sources come from?.
A primary source is a source that was created during the time period that we want to analyze or at a subsequent time by individuals who witnessed, participated in, and/or reflected on the events of that time.
Using primary sources, we analyze why the specific information was created and investigate how the information could uncover the event/history/culture and/or social norms. There are four common ways to find primary sources:
1) Check appendices, notes, and bibliographies
Secondary sources provide analysis, commentary, or criticism on primary sources. There is a rich list of primary sources under appendices, footnotes/endnotes, and bibliographies commonly in scholarly books.
2) Find primary sources using the UTL catalogue
When you search, you might include keywords/subjects, such as letter, correspondence, diaries, interviews, and pamphlets.
Check How to Find Primary Sources in the UTL LibrarySearch below 
3) Use databases that the University of Toronto Libraries offer
For example,
4) Use reliable online resources
For example,
5) Use images, maps, and songs, as primary sources
For example,
6) Visit the Thomas Fisher Rare Book Library, the University of Toronto.
The Thomas Fisher Rare Book Library has over 800 bound manuscript volumes representing a range of disciplines including history, theology, literature, philosophy, science, and medicine and in languages as diverse as Arabic, English, French, Ge'ez, German, Hebrew, Latin, and Persian, to name but a few. For Pre‐1600 Manuscripts in the Thomas Fisher Rare Book Library, please check the list.
The UTL LibrarySearch does not have a way to produce lists of primary sources. However, using one of the following words (Subject) in your search will help you find the source material you seek:
☆ An Example of How to Search ☆
Go to LibrarySearch (Advanced Search) and tweak Search filters. Choose Subject and enter the most important concept/person/theme in a search box. Select Books under Format
☆ NOTE ☆
Take advantage of Bibliographies and Reference lists in books and journal articles. In addition, use Oxford Bibliographies Online, they may give you the title of a primary source you can start searching for.
