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Common Fallacies: Contradiction

Contradiction is the most glaring type of fallacy. It is committed when two opposing statements are simultaneously asserted.
For example, saying “it is raining and it is not raining” is a contradiction. If the contradictions on the GMAT were this basic, the test would be significantly easier. Typically, however, the arguer obscures the contradiction to the point that the argument can be quite compelling. Take, for instance, the following argument:

We cannot know anything, because we intuitively realize that our thoughts are unreliable.

This argument has an air of reasonableness to it. But “intuitively realize” means “to know.” Thus the arguer is in essence saying that we know that we don’t know anything. This is self-contradictory.
In the game of basketball, scoring a three-point shot is a skill that only those with a soft shooting touch can develop. Wilt Chamberlain, however, was a great player, so even though he did not have a soft shooting touch he would have excelled at scoring three point shots.
Which one of the following contains a flaw that most closely parallels the flaw contained in the passage?
  1. Eighty percent of the freshmen at Berkeley go on to get a bachelor’s degree. David is a freshman at Berkeley, so he will probably complete his studies and receive a bachelor’s degree.
  2. If the police don’t act immediately to quell the disturbance, it will escalate into a riot. However, since the police are understaffed, there will be a riot.
  3. The meek shall inherit the earth. Susie received an inheritance from her grandfather, so she must be meek.
  4. During the Vietnam War, the powerful had to serve along with the poor. However, Stevens’ father was a federal judge, so Stevens was able to get a draft deferment.
  5. All dolphins are mammals and all mammals breathe air. Therefore, all mammals that breathe air are dolphins.
The argument clearly contradicts itself. So look for an answer-choice that contradicts itself in like manner.
Choice (A) is not self-contradictory. In fact, it’s a fairly sound argument—eliminate it.
Choice (B), on the other hand, is not a very sound argument. The police, though understaffed, may realize the seriousness of the situation and rearrange their priorities. Nevertheless, (B) does not contain a contradiction—eliminate it.
Choice (C), though questionable, does not contain a contradiction—eliminate it.
Choice (D), however, does contain a contradiction. It begins by stating that both the powerful and the poor had to serve in Vietnam and ends by stating that some powerful people—namely, Stevens—did not have to serve. This is a contradiction, so (D) is probably the answer.
Choice (E), like the original argument, is invalid but does not contain a contradiction—eliminate it. The answer is (D).

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