Fuzziness

In cognitive approaches to categorization, categories are argued to be blurred at the edges. Thus their boundaries display what has become known as fuzziness.

While cognitive linguists agree on the fuzziness of category boundaries, there are several theories as to the exact nature of the fuzziness.

Transition zones
The theory of transition zones holds that categories are separated by more or less fixed boundaries. However, these boundaries are not sharp dividing lines but rather transition zones in which categories graduate into each other. This often applies to entities that display a high level of vagueness.

Multiple parents
Multiple parenting implies that many concepts are actually hybrids in the sense that they inherit features from the schemas of two or more categories.

Mobile boundaries
The notion of mobile category boundaries implies that the placement of boundaries differs from individual to individual and from situation to situation, such that the same individual may place the boundaries of the same category differently in different situations. In this approach the placement of boundaries depends on context in the sense that in some situations an entity may be judsged as a member of a category, while in other situations, the same individual may judge the same entity as a non-member of the same category, or as a member of another category.

Boundaries as construal
In D.A. Cruse's construal-and-constraints model of semantics (e.g. Croft and Cruse 2004), categories are not fixed but dynamic, being construed online in accordance with contextual constraints. This approach is closely related to the notion of mobile boundaries mentioned above. However, in this aproach, boundaries, while a matter of context-induced construal, are not fuzzy as such. Construed boundaries are clear-cut, but they are not fixed.