The primary aim of a definition is to make a meaning understood, not merely to supply an additional fact about an existing object. If someone seeks the essential account of “human,” “rational animal” answers the relevant question.
“A human is in the market” supplies information about a person; it does not define the human species.
“A human is a rational animal” places the human within a genus and states the distinguishing feature.
A defining statement may resemble an ordinary proposition in form, but it has a different instructional purpose.