Prototype theory is a theory of categorization in cognitive science, particularly in psychology and cognitive linguistics, in which there is a graded degree of belonging to a conceptual category, and some members are more central than others. It emerged in 1971 with the work of psychologist Eleanor Rosch, and it has been described as a "Copernican revolution" in the theory of categorization for its departure from the traditional Aristotelian categories. It has been criticized by those that still endorse the traditional theory of categories, like linguist Eugenio Coseriu and other proponents of the structural semantics paradigm. In this prototype theory, any given concept in any given language has a real world example that best represents this concept. For example: when asked to give an example of the concept furniture, a couch is more frequently cited than, say, a wardrobe. Prototype theory has also been applied in linguistics, as part of the mapping from phonological structure to semantics. In formulating prototype theory, Rosch drew in part from previous insights in particular the formulation of a category model based on family resemblance by Wittgenstein (1953), and by Roger Brown's How shall a thing be called? (1958). Overview and terminology The term prototype, as defined in psychologist Eleanor Rosch's study "Natural Categories", was initially defined as denoting a stimulus, which takes a salient position in the formation of a category, due to the fact that it is the first stimulus to be associated with that category. Rosch later defined it as the most central member of a category. Rosch and others developed prototype theory as a response to, and radical departure from, the classical theory of concepts, which defines concepts by necessary and sufficient conditions. Necessary conditions refers to the set of features every instance of a concept must present, and sufficient conditions are those that no other entity possesses. Rather than defining concepts by features, the prototype theory defines categories based on either a specific artifact of that category or by a set of entities within the category that represent a prototypical member. The prototype of a category can be understood in lay terms by the object or member of a class most often associated with that class. The prototype is the center of the class, with all other members moving progressively further from the prototype, which leads to the gradation of categories. Every member of the class is not equally central