When you are trying to identify primary sources, think first-hand, contemporary, direct evidence or data, original records, artwork, writing, or research.
If someone is providing any kind of interpretation, summary, criticism, analysis, definition, or compilation of originals, you are probably straying into secondary or tertiary source territory.
Primary sources in the Sciences are a little different than primary sources in disciplines like the Humanities or the Arts.
In the Sciences, primary sources can include resources such as correspondences, letters, lab reports, etc., but more often than not, looking for primary sources will mean finding information or literature on original research.
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