Full Idea
It would be strange for a natural scientist to know what the sun and the moon are, but to be completely ignorant about their necessary attributes.
Gist of Idea
Scientists must know the essential attributes of the things they study
Source
Aristotle (Physics [c.337 BCE], 193b27)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.36
A Reaction
This nicely captures the common sense idea of essentialism - that we must know the essential features of things, and ignore the incidental ones (like sunspots, or phases of the moon).