In the mid 1970’s, a prototype approach to meaning was suggested by Eleanor Rosch. Rosch conducted psycholinguistic research on the internal structure of categories and the influence of categories on word meaning. This research has proven to be very important to the field of semantics. People think in categories and categories underlie much of our vocabulary and much of our reasoning. Rosch concluded that people assign an object to a category by comparing that object to their view of the best exemplar associated with the category. Rosch further added “the task of category systems is to provide maximum information with the least cognitive effort.”
Take the category of birds as an example. We know that birds generally have feathers and a beak, lay eggs, fly and eat worms. A robin is a fairly prototypical bird but an ostrich is not because ostriches don't fly and they are larger than the average bird. And how about ducks? We don't typically think of fish-eating and water-floating when we think of birds.
The following are features of prototypicality:
1. Members of a category do not always share the same amount of features.
2. The structure of categories takes the form of a set of clustered and overlapping meaning.
3. Categories exhibit degrees of membership.
4. Categories have fuzzy boundaries.
As far as the way people measure similarities when determining category membership, appearance plays an important role for some categories while in others similarity can be judged by degree of variation and/or influence of use.