Lecture Tuesday 22 March 2005

Classification made simple


things to take out of your house in a fire
Do we have a word for this?
No.
But we have a word for "cat" representing things that are cat.

This is an ad hoc category: highly situational, improvised as necessary

What is an essential difference between an ad hoc category and a named one?

What I would remove:
family & pets
fire box
computer
old tax records
pieces of art
photo albums



we also have:
- scientific/expert classes
- folk/everyday classes
- class by definition (arbitrary)

coherence/convergence - ad hoc classes are difficult to converge

defining a class
----------------
extensional - listing all members
intensional - listing essential properties/conditions that members must meet (the rules)
subjective
intensional -



mutually exclusive classes are wonderful but really don't happen very much in reality or if they do they're quite unwieldly

exhaustive classes are all-inclusive; the category "other" contitutes a failure

hierarchical classifications are too rigid; often classifications depend upon multiple layers of characteristics