In Philosophy, primary sources can include: Philosophical texts, treatises, meditations, personal narratives, diaries, memoirs, correspondence, letters. Most frequently the works of the philosopher him/herself, though letters, lectures, and contemporary criticism may also be useful primary materials depending on your exact interest.
Don't understand the difference between primary and secondary sources? Watch this video that provides explanations of differences.
There is an increasing amount of digitized primary source material available in library databases and on the web from libraries, museums, educational institutions, and more. Explore these resources to find texts, images, and much more on this topic.
Here are a few examples of books: