Full Idea
For Aristotle, to give a definition one must first state the genus and then the differentia of the kind of thing to be defined.
Clarification
'Genus' is category; 'differentia' are distinguishing marks within the category
Gist of Idea
Aristotelian definition involves first stating the genus, then the differentia of the thing
Source
report of Aristotle (works [c.330 BCE]) by J.O. Urmson - Aristotle's Doctrine of the Mean p.157
Book Reference
'Essays on Aristotle's Ethics', ed/tr. Rorty,Amélie Oksenberg [University of California 1980], p.157
A Reaction
Presumably a modern definition would just be a list of properties, but Aristotle seeks the substance. How does he define a genus? - by placing it in a further genus?
Related Idea
Idea 4385 Aristotelian definition involves first stating the genus, then the differentia of the thing [Aristotle, by Urmson]