The difference between primary and secondary sources
Launch library · evergreen read
A primary source is direct evidence: original data, a firsthand account, or the original document itself. A secondary source discusses or interprets that evidence after the fact, adding useful context but also adding a layer of interpretation between the reader and the original material being described, a layer that can subtly shift meaning along the way.
Neither type is automatically more trustworthy, since a poorly conducted primary study can be less reliable than a careful secondary summary of many studies together, but knowing which type of source you are looking at helps you judge what kind of scrutiny it actually needs before relying on it.
Tracing a claim back toward its primary source, where practical, is a useful habit, since each retelling of a fact carries some risk of simplification or distortion, and the original material often contains caveats and context that later summaries can quietly drop along the way to a reader.