Secondary sources are works that are based on analysis of primary sources, such as textbooks, biographies, nonfiction books about history and monographs. Many secondary sources in history include quotations from primary sources or illustrations that constitute primary sources. In literary research, secondary sources include works of literary theory or literary scholarship (found in scholarly journals or specialized books).
Sometimes a source can be both primary and secondary. if one is using census data from the 1855 US census as support for an argument on poverty in American literature, then the census is a secondary source; but if one is analyzing the census itself, then the census is a primary source.
