If you weigh the same as a duck, then, logically, you’re made of wood and must be a witch. Or so goes the reasoning of Monty Python’s Sir Bedevere. Obviously something has gone wrong with the knight’s reasoning – and by the end of this lesson, you’ll know exactly what that is. This lesson will focus on 10 fallacies that represent the most common types of mistakes in reasoning.
Objectives
In this lesson students will:
- Learn to distinguish between different types of fallacies and booby traps.
- Assess short arguments for examples of fallacious reasoning.
- Analyze longer arguments for instances of fallacies or other booby traps that might hinder good reasoning.
KEY TERMS:
- Argument: a conclusion together with the premises that support it
- Premise: a reason offered as support for another claim
- Conclusion: a claim that is supported by a premise
- Valid: an argument whose premises genuinely support its conclusion
- Unsound: an argument that has at least one false premise
- Fallacy: an argument that relies upon faulty reasoning
- Booby trap: an argument that, while not a fallacy itself, might lead an inattentive reader to commit a fallacy.
Example 1: Whichever basketball team scores the most points will win the game. Virginia scored more points than UNC. Therefore Virginia won the game.
In Example 1, the first two sentences are premises and the third is the conclusion. The argument is valid, for the two premises provide genuine support for the conclusion.
Example 2: Whichever candidate receives the greatest share of the popular vote will be elected president of the United States. Al Gore received more votes than George Bush. Therefore, Al Gore was elected president of the United States.
Example 2 has exactly the same structure as Example 1. The first two sentences are premises, and the third sentence is the argument’s conclusion. The difference, of course, is that in Example 2, the first premise is false. Getting the most votes is not the way one gets elected president. So Example 2 is unsound.