The Fallacy of False Dichotomy
We have decided to create a new category on our site: fallacies. From time to time, we will add posts about specific fallacies or fallacies in the news. We will start today with the fallacy of false dichotomy.
A disjunctive syllogism is a common argument form with the following structure:
(1) Either p is true or q is true.
(2) p is not true.
Therefore, q is true.
The disjunctive syllogism does not tell us that p is true, or that q is true: it tells us that one or the other is true. This form of argument commits the fallacy of false dichotomy when its disjunctive premise (1) is false.
Consider the following well-known example:
“Either you are with us, or you are with the terrorists.” – George Bush (here)
(1) Either you are with us, or you are with the terrorists.
(2) You are not with us.
Therefore, you are with the terrorists.
The problem with this argument is that (1) is not true: it does not exhaust all possible options. A person may, say, oppose the war in Iraq without supporting the terrorists. It does not follow from the fact that a person does not support an American policy or war that he or she supports the terrorists.
Source:
Irving M Copi, Carl Cohen, and Daniel E. Flag. Essentials of Logic (Second Edition). (Upper Saddle River: Pearson, 2007), 75-76.
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