Full Idea
A real definition, according to the Aristotelian tradition, gives the essence of the kind of thing defined. Man is defined as a rational animal, and thus rationality and animality are of the essence of each of us.
Gist of Idea
Aristotelian definitions aim to give the essential properties of the thing defined
Source
report of Aristotle (works [c.330 BCE]) by Willard Quine - Vagaries of Definition p.51
Book Reference
Quine,Willard: 'Ways of Paradox and other essays' [Harvard 1976], p.51
A Reaction
Compare Idea 4385. Personally I prefer the Aristotelian approach, but we may have to say 'We cannot identify the essence of x, and so x cannot be defined'. Compare 'his mood was hard to define' with 'his mood was hostile'.