An Introduction to Classification and Clustering
An intelligent being cannot treat every object it sees as a unique entity unlike anything else in the universe. It has to put objects in categories so that it may apply its hard-won knowledge about similar objects encountered in the past, to the object at hand.
Steven Pinker, How the Mind Works, 1997.
One of the most basic abilities of living creatures involves the grouping of similar objects to produce a classification. The idea of sorting similar things into categories is clearly a primitive one since early man, for example, must have been able to realize that many individual objects shared certain properties such as being edible, or poisonous, or ferocious and so on.
Classification, in its widest sense, is needed for the development of language, which consists of words which help us to recognize and discuss the different types of events, objects and people we encounter. Each noun in a language, for example, is essentially a label used to describe a class of things which have striking features in common; thus animals are named as cats, dogs, horses, etc., and such a name collects individuals into groups. Naming and classifying are essentially synonymous.
As well as being a basic human conceptual activity, classification is also fundamental to most branches of science. In biology for example, classification of organisms has been a preoccupation since the very first biological investigations. Aristotle ...