When inferences are defective, they are called fallacious. When defective styles of reasoning are repeated over and over, because people often get fooled by them, then we have an argumentative fallacy that is worth flagging with a name. The number and variety of argumentative fallacies are limited only by the imagination. Conse quently, there is little point in trying to construct a complete list of fallacies. What is crucial is to get a feel for the most common and most seductive kinds of fallacy. Once this is done, we should be able to recognize many other kinds as well. The goal of Part IV is to develop that skill.
This chapter examines one of the main ways in which arguments can be defective or allacious because language is not used learly enough for the context. This kind of unclarity is vagueness. Vagueness occurs when, in a given context, a term is used in a way that allows too many cases in which it is unclear whether or not the term applies. Vagueness underlies several common fallacies, including three kinds of slippery-slope arguments.