What counts as original evidence varies by subject. You may be familiar with primary sources for history, in which sources created at the time studied often provide the direct, first-hand account that historians study. For different subjects, primary sources will be different.

Examples of Primary and Secondary Sources

The table below shows examples of primary and secondary sources for different subjects.

Primary and Secondary Source Examples by Subject
Subject	Primary Source	Secondary Source
Science, Social Science	Peer-reviewed research articles, technical reports Ex. Original research article about Lyme disease	Articles summarizing or discussing the results of original research Ex. Article reviewing the research on Lyme disease
History	Diaries, letters, original documents, newspapers Ex. Supreme Court opinion for Plessy v. Ferguson	Biographies, books, journal articles Ex. Legal analysis of the Supreme Court opinion for Plessy v. Ferguson
Arts	Music scores, images, performance reviews Ex. Original choreography for Romeo and Juliet	Stylistic analysis, biographies, journal articles Ex. Analysis of contemporary dance in early 1900s
English	Original works of literature, poetry Ex. Leo Tolstoy’s War and Peace	Analysis or commentary on primary sources Ex. Journal article about Leo Tolstoy’s War and Peace
Philosophy	Original texts, treatises, meditations, lectures Ex. Hegel’s Phenomenology of Spirit	Criticisms in personal letters before 1900; After 1900, journal articles and books Ex. Analysis of the Hegelian Dialectic

Finding Primary Sources

Since different subjects have different primary sources, you will first need to determine what kind of primary source you’re looking for. Then you can choose a library search tool. If you have questions about where to look for primary sources for your subject, talk to a librarian.