Critical Thinking by Example

Post Hoc Fallacy This fallacy occurs when the fact that event A precedes event B in time is said to be sufficient evidence that A causes B. Although causes typically proceed effects in time, we can see in example 7.5 that establishing that one event proceeds the other in time is not sufficient to show that there is a causal relationship; in particular, it may simply be a coincident that I washed my car and then it rained.
Example 7.5 P1: I washed my car. P2: It then rained. C: Washing my car caused it to rain.
Fallacy of Jumping from Correlation to Causation This fallacy occurs when the correlation of two event types, A and B, is cited as sufficient evidence that A causes B. As example 7.6 illustrates, even if two events are perfectly correlated, if unemployment always goes down after the Democrats win, this in itself does not show that a Democratic victory is the cause of reduced employment. For example, it might be the case that there is a business cycle where unemployment regularly goes up and down, and that high unemployment causes the Democrats to win.	Example 7.6 P1: Every time the Democrats win, unemployment goes down. C: The Democrats being in power causes lower unemployment rates.
Fallacy of Improper Sampling This fallacy occurs when the sample cited in the premise set does not properly represent the population cited in the conclusion. In example 7.7 we can see that the population described in the conclusion is women, that is, the conclusion says something about how women in general view their husbands’ contribution to household chores. The sample, however, is taken from subscribers of Women’s Good Housekeeping Magazine. We have no evidence that those that subscribe to this magazine are representative of women in general. Perhaps subscribers are wealthier than average, or they are in more “progressive” relationships. A better way to support the conclusion would be to take a random sample of women in general.	Example 7.7 P1: In a random telephone survey of subscribers, Women’s Good Housekeeping Magazine found that 93% of all married women believe that their husbands do an equal amount of the household chores. C: It is false that women think that men do not do an equal amount of the household chores.