Sometimes called by its Latin name pars pro toto, this fallacy is closely related to hasty generalization. In this fallacy, arguers pick out a part of the whole or a sample of the whole (often not a typical or representative part or sample) and then claim that what is true of the part is true for the whole.

Part for the Whole

Sometimes called by its Latin name pars pro toto, this fallacy is closely related to hasty generalization. In this fallacy, arguers pick out a part of the whole or a sample of the whole (often not a typical or representative part or sample) and then claim that what is true of the part is true for the whole. If, say, individuals wanted to get rid of the National Endowment for the Arts (NEA), they might focus on several controversial programs funded by the NEA and use them as justification for wiping out all NEA programs. The flip side of this fallacy occurs when an arguer picks only the best examples to make a case and conveniently forgets about examples that may weaken the case.

Post Hoc, Ergo Propter Hoc

The Latin name of this fallacy means “after this, therefore because of this.” The fallacy occurs when a sequential relationship is mistaken for a causal relationship. (See Chapter 12page 259, where we discuss this fallacy in more depth.) For example, you may be guilty of this fallacy if you say, “Cramming for a test really helps because last week I crammed for my psychology test and I got an A on it.” When two events occur frequently in conjunction with each other, we’ve got a good case for a causal relationship. But until we can show how one causes the other and until we have ruled out other causes, we cannot be certain that a causal relationship is occurring. For example, the A on your psych test may have been caused by something other than  your cramming. Maybe the exam was easier, or perhaps you were luckier or more mentally alert. It is often difficult to tell when a post hoc fallacy occurs. When the New York police department changed its policing tactics in the early 1990s, the crime rate plummeted. But did the new policing tactics cause the drop in the crime rate? Many experts suggested other clauses, including economist Steven Levitt, who attributes the declining crime rate to the legalization of abortion in the 1970s (and hence to a decline in unwanted children who might grow up to be criminals).