A primary source provides direct or firsthand evidence about an event, object, person, or work of art. In the natural and social sciences, primary sources are often empirical studies—research where an experiment was performed or a direct observation was made. The results of empirical studies are typically found in scholarly articles or papers delivered at conferences.
Secondary sources describe, discuss, interpret, comment upon, analyze, evaluate, summarize, and process primary sources. Secondary source materials can be books or articles in encyclopedias, newspapers, or popular magazines, or articles found in scholarly journals that discuss or evaluate someone else's original research.