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Fallacies

A fallacy is a defect in an argument other than its having false premises.   Fallacies are divided into two types: formal and informal.   A formal fallacy is a fallacy that can be identified by inspecting the form of the argument.   Any argument that has an invalid form has committed a formal fallacy.   For example: "All A are B; all A are C; therefore all B are C" contains a formal fallacy. An informal fallacy is a fallacy that, in order to be identified, requires an analysis of the content of the argument and not just an inspection of the form of the argument. For example, "George Bush is no friend of mine; no friend of mine is a Chinese communist; therefore, George Bush is a Chinese communist." While it may appear to have a valid form, it is clearly fallacious.   Because detecting the fallaciousness of this argument depends on understanding the content—in particular the meaning of "no friend of mine"—the argument contains an informal fallacy.



Informal fallacies can be classified in a number of ways.   This list contains 22 informal fallacies, divided into five groups: fallacies of relevance, weak induction, presumption, ambiguity, and grammatical analogy. Note: Your text lists others as well as variant names for some of these. Don't get confused. J



Fallacies of relevance apply to arguments with premises that are not logically relevant to the conclusion but that are psychologically relevant to the conclusion in such a way as to make the conclusion appear to follow from them. The eight fallacies of relevance are:



Appeal to force—when the arguer, instead of providing genuine evidence for a conclusion, uses some sort of threat of harm to the listener if the conclusion isn't accepted.   "If you don't accept my argument, I'll punch you."
Appeal to pity—when the arguer, instead of providing genuine evidence for a conclusion, attempts to get the conclusion accepted by evoking pity from the listener.   "If you don't give me a raise, my 12 children will...