Category Errors

A category error occurs when someone acts as though some object had properties which it does not or cannot have. The reason why it cannot have those properties is because the properties belong to objects in some other category or class. For example:

Colorless green ideas sleep furiously.

The above sentence commits at least two category errors. One is the attribution of the property of color (green) to something immaterial (ideas). This is an example of a property (color) which "ideas" cannot have. A second is the attribution of a property of speed/manner (furiously) to an action (sleep). This is an example of a specific property which sleep does not have, even though sleep can have other, similar properties - like soundly or quickly.

For Aristotle, a category error was just a form of equivocation, but it plays a much larger role in the philosophy of Ryle. Accordin to Ryle in his book The Concept of Mind, "Philosophy is the replacement of category-habits with category-disciplines..." Thus, good philosophical thinking is a matter of adopting a proper theory of categories. In this way, unwarranted beliefs are a result of improper thinking about categories.