Critical Thinking by Example

7.2 Fallacies of Sufficiency

Fallacy of Hasty Conclusion An argument contains this fallacy if the premise set (even if true) is insufficient to warrant the acceptance of the conclusion. Note: the remaining fallacies of sufficiency are specific forms of this fallacy. On quiz material, you should choose this fallacy only if none of the other six fallacies are appropriate.	Example 7.3 “All the polar bears we saw at the zoo today are white. So, many polar bears are white.”
Fallacy of Hasty Generalization An argument contains this fallacy if the premise set (even if true) is insufficient to warrant the acceptance of the generalization.	Example 7.4 “All the polar bears we saw at the zoo today are white. So, all polar bears are white.”
Fallacy of Affirming the Consequent This fallacy is committed when the necessary condition in a conditional argument is cited as sufficient for the conclusion. Note that the fact that it is cloudy is relevant to the conclusion that it is rainy. Imagine someone trying to prove to you that it is rainy. The fact that it is cloudy would provide some evidence that it is rainy, even though the presence of clouds is not in itself sufficient evidence.	Example 7.5 P1: If it is rainy, then it is cloudy. P2: It is cloudy. C: So, it is rainy.
Fallacy of Denying the Antecedent This fallacy is present when the denial of the sufficient condition in a conditional argument is cited as sufficient for the conclusion. Note that the premise set is relevant to the conclusion in example 7.4 The fact that it is not rainy provides some evidence that it is not cloudy, even though the absence of rain is not sufficient for it not being cloudy.	Example 7.6 P1: If it is rainy, then it is cloudy. P2: It is not rainy. C: It is not cloudy.