It is not always easy to separate fact from opinion. Skilled writers can make you think their interpretations are facts. Assumptions should be reasonable. Note errors or omissions. You should explore enough sources to obtain a variety of viewpoints.
Primary sources are the raw material of the research process.
Secondary sources are based on primary sources. Books, encyclopedia articles, and scholarly journal articles about a subject would be considered secondary sources. Choose both primary and secondary sources when you have the opportunity. Evaluative Reviews Locate critical reviews of books in periodical indexes, such as The Art Index, Bibliography of the History of Art , or the Book Review Digest. If so, locate these sources for more information on your topic.