A secondary source of information is necessary to support a thesis statement when a student wants to explore outside influences on a literary work.
Primary sources come directly from original sources, documents, pictures or photographs, and other first-hand sources. These are considered to give accurate facts about a topic.
Secondary sources tend to be more subjective, for example a review of a book, film, or theatrical piece might be considered a secondary source because it is more subjective, but still gives relevant information about the topic.