Ian Jarvie  

"Essentialism is the doctrine that things have essences that maintain their identity through change. It comes in many versions, from Plato’s unchanging ideas, to Kripke’s rigid designators that stay with things through all possible worlds. Its methodological form is the search for the essence among all the properties of things, or the search for an encapsulating definition specifying necessary and sufficient conditions for the use of a term. A formula that describes the essence of a thing is its definition; it sharpens and fixes our intuition of what it really is." --"Pornography Stumps Analytic Philosophers of Art", 2015, Ian Jarvie