Re: Categorisation and Prototypes

From: Naden, Christopher (
Date: Mon May 27 1996 - 04:39:43 BST

Q.30: What is the evidence for the prototype theory of categorisation?

Categorization is the practice of sorting things: making groups of
similare objects. The classical theory of categorzation suggests that
the way we do this is to learn a list of necessary and sufficient
features with which to classify categories. For example, the features
of the category mammal are [a] Give birth to live young, and [b] suckle
their young on milk. Each of these features are necessary, in other
words anything lacking them is not a mammal, but neither are
sufficient: in other words BOTH are needed to indicate mammal status,
one alone will not do.
The Prototype theory of categorization suggests that instead of this
feature analysis method, we in fact categorize by learning a
"prototype", an 'ideal' image of the perfect member of that category,
against which we match propective members. If, for example, we are
categorizing a swallow, it is closer to the 'prototype' image of the
category 'bird' than to the 'prototype' image of the category 'camel':
thus it gets categorized as a bird. The evidence for this theory was
propoed in 1978 buy Eleanor Rosch, who noted that not only do people
not always know the features by which they classify categories, but
they find that certain members of categories semm to be 'more typical'
than others (a swallow seems a more typical 'bird' than and ostrich).
She also noted that they tend to classify these more 'typical' examples
quicker than less typical ones.
Further evidence for the prototype theory was added by Ludwig
Witgenstein when cited the example of the category 'game'. It is
clearly a category, yet no-one can actualy point out the necessary and
sufficient features of the category.
The 'protoype' theory only really applies consistenly to categories
which are a matter of degree: for example the category 'long'. It would
be difficult to build up a list of features for this category as it is
not only continuous but relative; however a prototype against which
each example could be checked might make this easier to categorize.

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