Editing Definition (section)

===Nominal definitions vs real definitions===
{{Main|Essence}}
In classical thought, a definition was taken to be a statement of the essence of a thing. [[Aristotle]] had it that an object's essential attributes form its "essential nature", and that a definition of the object must include these essential attributes.<ref>[[Posterior Analytics]], Bk 1 c. 4</ref>

The idea that a definition should state the essence of a thing led to the distinction between ''nominal'' and ''real'' essence—a distinction originating with Aristotle. In the [[Posterior Analytics]],<ref>[[Posterior Analytics]] Bk 2 c. 7</ref> he says that the meaning of a made-up name can be known (he gives the example "goat stag") without knowing what he calls the "essential nature" of the thing that the name would denote (if there were such a thing). This led medieval logicians to distinguish between what they called the ''quid nominis'', or the "whatness of the name", and the underlying nature common to all the things it names, which they called the ''quid rei'', or the "whatness of the thing".<ref>. Early modern philosophers like Locke used the corresponding English terms "nominal essence" and "real essence".</ref> The name "[[hobbit]]", for example, is perfectly meaningful. It has a ''quid nominis'', but one could not know the real nature of hobbits, and so the ''quid rei'' of hobbits cannot be known. By contrast, the name "man" denotes real things (men) that have a certain ''quid rei''. The meaning of a name is distinct from the nature that a thing must have in order that the name apply to it.

This leads to a corresponding distinction between ''nominal'' and ''real'' definitions. A nominal definition is the definition explaining what a word means (i.e., which says what the "nominal essence" is), and is definition in the classical sense as given above. A real definition, by contrast, is one expressing the real nature or ''quid rei'' of the thing.

This preoccupation with essence dissipated in much of modern philosophy. [[Analytic philosophy]], in particular, is critical of attempts to elucidate the essence of a thing. [[Bertrand Russell|Russell]] described essence as "a hopelessly muddle-headed notion".<ref>''A History of Western Philosophy'', p. 210.</ref>

More recently [[Kripke semantics|Kripke's]] formalisation of [[possible world]] semantics in [[modal logic]] led to a new approach to [[essentialism]]. Insofar as the essential properties of a thing are ''necessary'' to it, they are those things that it possesses in all possible worlds. Kripke refers to names used in this way as [[rigid designator]]s.