Sunday, March 21, 2010

Nine Common Fallacies of Logic

There are plenty of tools you can use to persuade your readers. But there is a right way and a wrong way to make an argument. That's why all writers should have an understanding of the key logical fallacies that can trip up even the most carefully edited article.

Familiarize yourself with the following flaws of reasoning. You'll tighten up your own logic and you'll be on guard when others use these suspect tactics.

Ad Hominem Argument
Arguing that a person's argument is flawed because of an untrue or irrelevant detail about that person. Barack Obama is a Muslim, therefore he will be soft on terrorism.

Slippery Slope Fallacy
Arguing that adopting some policy will cause negative consequences without making a case for how or why those consequences would happen. If we legalize assault rifles, pretty soon people will be carrying howitzers down the street! Never mind that a person can't carry a howitzer.

Straw Man Argument
Setting up an extreme, caricatured, or distorted version of your opponent's argument that you can easily knock down, and using that as proof that the entire argument is wrong.

Red Herring
Introducing irrelevant facts or unrelated issues as support for or against an argument. The Republicans claim that education budgets must be cut, but how can we take school lunches away from our underprivileged children? Never mind that the details of the budget cuts (and whether they actually eliminate school lunches) are missing from this statement.

Use of Weasel Words
Using phrases such as experts believe or it is widely thought in an attempt to bolster an argument. Which experts? Exactly how widely thought? Also known as the False Authority Fallacy.

Arguing From a Preconceived Premise
Did you decide what your position was before you started looking at the facts and evidence? Almost no one admits to this sin of logic, yet most of us are guilty of it at one time or another.

Massaging, Arranging, Distorting or Omitting Facts to Fit a Conclusion
The sad thing about this particular logic infraction is how common it is. For 300 pages of excellent examples, see Manufacturing Consent by Edward Herman and Noam Chomsky.

Appealing to Widespread Belief
Everyone thinks that... Just because a lot of people think or believe something doesn't make it true.

Arm-Waving, or Proof by Vigorous Assertion
Repeating the same arguments over and over again, or making statements like this conclusion is so clear that only a fool wouldn't grasp it.

There are many more examples of unethical logic, but these are some of the most common. We'll discuss the ethics of sound logic in our next post.