Taxonomy of Fallacies

There are a number of competing and overlapping ways to classify fallacies of argumentation. For example, they can be classified as either formal or informal. A formal fallacy can be detected by examining the logical form of the reasoning, whereas an informal fallacy depends upon the content of the reasoning and possibly the purpose of the reasoning. The list below contains very few formal fallacies. Fallacious arguments also can be classified as deductive or inductive, depending upon whether the fallacious argument is most properly assessed by deductive standards or instead by inductive standards. Deductive standards demand deductive validity, but inductive standards require inductive strength such as making the conclusion more likely. Fallacies can be divided into categories according to the psychological factors that lead people to commit them, and they can also be divided into categories according to the epistemological or logical factors that cause the error. In the latter division there are three categories: (1) the reasoning is invalid but is presented as if it were a valid argument, or else it is inductively much weaker than it is presented as being, (2) the argument has an unjustified premise, or (3) some relevant evidence has been ignored or suppressed. Regarding (2), a premise can be justified or warranted at a time even if we later learn that the premise was false, and it can be justified if we are reasoning about what would have happened even when we know it didn't happen.

Similar fallacies are often grouped together under a common name intended to bring out how the fallacies are similar. Here are three examples. Fallacies of relevance include fallacies that occur due to reliance on an irrelevant reason. In addition, ad hominem, appeal to pity, and affirming the consequent are some other fallacies of relevance. Accent, amphiboly and equivocation are examples of fallacies of ambiguity. The fallacies of illegitimate presumption include begging the question, false dilemma, no true Scotsman, complex question and suppressed evidence. Notice how these categories don't fall neatly into just one of the categories (1), (2), and (3) above.