Human categorisation is one of the major issues in Linguistics. The ability to categorise, i.e., to judge that a particular thing is or is not an instance of a particular category, is an essential part of cognition. Categorisation is often automatic and unconscious, except in problematic cases. This can cause us to make mistakes and make us think that our categories are categories of things, when in fact they are categories of abstract entities. When experience is used to guide the interpretation of a new experience, the ability to categorise becomes indispensable.
The classical view on categorisation, that of Aristotle, claims that categories are defined in terms of a conjunction of necessary and sufficient binary features, that is to say that linguistic analytical categories impose a set of necessary and sufficient conditions for the membership in the category. This requirement not only implies that categories have clear boundaries and that all members of a category have equal status but also that there is an abstract, general definition with which all the members of that category must comply.
Instead of relating these different senses to an abstract default sense that includes all of them, the cognitive approach adopts a prototype categorization model. In this model human categories have two types of members: the ‘prototype’ and several less-central members related to the former in a motivated way. The prototype is the best, the most prominent and the most typical member of a category.