10 Logical Lies

10. Circular Argument / Slippery Slope

When an argument is circular, it means it's not valid. The argument is "circular" in the sense that something about the conclusion is already included in the premise. What does that mean?

A premise is how you "set up" your argument. For example, "Being elected the prime minister of England means that people trust you." The premise is where you establish your facts. There's nothing really wrong with this premise, as long as you understand it to really mean "a majority of Britons," until you use it to come to the following conclusion:

"Therefore, people should trust the prime minister of England." This conclusion is not supported by the fact that, to be elected, at some point, a prime minister was trusted by a majority.

Related to this problem of circular argument is the "Slippery Slope" argument, in which a person might suggest that disastrous things will happen if his or her side loses this argument. For example, "If we cut the library budget here in our town, in 25 years nobody in America will be reading anymore!"

As with the "Circular Argument," the person using the "Slippery Slope" argument is assuming that he or she is right, instead of really proving it.

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