angles that sum to 180 degrees. To see if something is a triangle one has only to check for
these properties, and if one is missing, one does not have a triangle (Medin, 1989).
There is evidence that people can treat concepts in ways which agree with the classical
view (Bruner et. al. 1956). However, Bruner's et. al. work was carried out in a domain of
fairly artificial categories. This view does not apply to natural categories which appear to
categorize entities according to a set of necessary and sufficient conditions. Also, some
other serious problems with the classical view, are that it fails to specify defining concepts
eg. someone may list "made of wood" as a necessary property for violins, but not all
violins are made of wood.
2.2.3.1.2 The Probabilistic view theories
The rejection of the classical view of categories has been associated with the ascendance
of the probabilistic view of category structure by Wittgenstein (1953). The term
probabilistic view, seems to imply that people organize categories via statistical reasoning
(Oden & Lopes 1982). Probabilistic view categories are organized according to a family
resemblance principle. That principle holds that categories are fuzzy or ill-defined and
that they are organized around a set of properties or clusters of correlated attributes that
are only characteristic for category membership (Rosch, 1978).
According to family resemblance relationship, each member of a category has at least one,
and probably several, attributes in common with one or more members, but that no or few
attributes are common to all members of the category (Rosch and Mervis 1975; Mervis
& Rosch, 1981). Rosch and Mervis (1975) provided considerable empirical support for
this position for natural concepts (e.g. colours). In its place a new way of explaining
category formation, was provided - what Rosch has termed the theory of prototypes and
basic level categories. A prototype is a representation which captures many of the common
features of a group, and can be used to decide category membership (Rosch, 1978; Rosch,
Mervis, 1975; Rosch, Mervis, Gray, Johnson, 1976; Smith, Medin, 1981).
Rosch & Mervis (1975) suggest that word meaning is not specifically tied to clear
definitions. Instead the referents of a word may share some but not all of a set of common
features. For example, penguins which belong to the category of birds have feathers and
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