Quite often you will be expected to use "scholarly" or "peer-reviewed" sources. How can you tell whether a source is scholarly? Look for these indicators.
Though many databases let you limit a search to scholarly articles, they aren't foolproof. As an example, they will include book reviews, which are not reporting original research and may not be what your course instructor has in mind. When in doubt, check with your professor. And take a look at "Anatomy of a Scholarly Article" from North Carolina State University Library.
The term "primary source" is defined differently by different disciplines. In the humanities, a primary source is a historical document, such as a diary, memoir, a work of art, a news account published when an event was fresh - something from the historical period under examination, unfiltered by anyone else. In the sciences, a primary source is a scientist's write-up of their research that includes their methods and results, as opposed to science journalism or a summary of research (a "review article") that has been conducted to provide an overview of research on a given topic.
A secondary source is one that has already been analyzed by someone else.Moving even further from the unfiltered event is a teriary source such as a textbook, that summarizes knowledge in general terms.
Using primary sources, whether in science or the humanities, helps a researcher get as close as possible to the subject under examination. Using primary sources can be a good way to point your reader to the raw materials of your ideas and provide an opportunity for you to do your own, original analysis.
To find historical primary sources, check out our guide to primary sources available in our library.