False Dichotomy / Black & White Thinking


The argument tries to force a conclusion by offering (or implying) an incomplete list of alternatives. Typically only two options are considered, while in fact a number of additional options are available.



A particularly important sub-category of this fallacy - almost common enough and important enough to deserve its own name - is the fallacy of arguing that since we cannot entirely eradicate a problem, we should therefore do nothing about it at all. This is sometimes called "making the perfect the enemy of the good."



"We shouldn't prevent all citizens from owning guns. Hunters and gun collectors have a perfect right to own weapons. Therefore gun control laws of any kind are a bad idea.


"My contribution to the Red Cross won't solve the problem of world hunger, so it won't do any good. I won't bother to make a contribution at all."



Black & White Thinking - the fallacy of leaping from the falsity (or undesirability) of one proposition to the truth (or desirability) of an extreme opposite - is identical in its basic logical structure to False Dichotomy. Both employ reasoning by process of elimination - a perfectly valid form of reasoning known to logicians as Disjunctive Syllogism (the moden name for the form "Modus Tollendo Ponens" as it was known to the ancient Stoics):

Either p or q. Not p. Therefore q.

The flaw, of course, is that the disjunction (or choice) as stated in the major premiss, is incomplete, so eliminating one option does not necessitate the adoption of the alternative. The fallacy, of course, seems convincing (and so mimics good reasoning) because reasoning by elimination is a perfectly sound procedure, provided all the possible alternatives are considered.

The subtle distinction between False Dichotomy and Black & White Thinking can be explained by considering how an argument would appear when stated as an enthymeme (i.e. an argument in which one of the necessary premisses is merely implied but left unstated. Consider:

Thelma (to Louise): "Either we drive this car over the cliff or we return home to our old lives. Let's drive over the cliff."

Thelma (to Louise): "Well, we can't return home to our old lives! Let's drive this car over the cliff."

In the first passage, the alternatives are explicitly stated, so the argument presents itself as a fallacy of False Dichotomy. In the second passage, the falsity of one position is explicitly stated, so the argument presents itself as a fallacy of Black & White Thinking. However, the arguments are actually identical to each other, once the necessary missing premisses are added. Hence, while False Dichotomy and Black & White Thinking can seem like distinct fallacies, on technical grounds, it is clear that they are not. Both turn on the falsity of the alternatives under consideration.


Source: The fallacy is described in Antoine Arnauld and Pierre Nicole, L'Art de Penser (The Art of Thinking), 1662, better known as the Port-Royal Logic. There it is called "overlooking an alternative."


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