Primary vs. Secondary Sources

A source's own type doesn't just describe where a fact came from — it determines what claim that source can actually support. This chapter covers the real taxonomy, a genuinely common point of confusion within it, and a real, documented case where getting this distinction wrong let a deliberately flawed study reach millions of readers.

A Real, Cross-Disciplinary Taxonomy

• Primary source: original, firsthand material — raw data, an original research article reporting new findings, a historical document, an eyewitness account, an artifact, an interview transcript.
• Secondary source: analysis or interpretation built on primary sources — a textbook chapter, a review article synthesizing many studies, a news article reporting on someone else's research.
• Tertiary source: a compilation or summary of secondary sources — an encyclopedia entry, a bibliography, many general reference works.

The Same Kind of Article Can Be Either

A genuinely common point of confusion: "peer-reviewed journal article" isn't itself a source type. An original research article reporting new data is a primary source. A review article or meta-analysis, even in the exact same journal, synthesizing dozens of other studies without collecting any new data of its own, is a secondary source. Confusing the two matters — a review article can only ever be as reliable as the primary studies it draws on, and citing it as though it were itself original evidence skips a real, necessary evaluation step.

A Real Case Where the Distinction Mattered

The published article was, technically, a genuine primary source — it reported original data from a real study. But it was a deliberately unreliable one. That distinction matters: being a primary source describes where a claim came from, not whether the claim is trustworthy.

Hands-On Exercises