Philosophy 103 - Introduction to Logic: Critical Thinking

2/02 - Informal Fallacies II


Fallacies of Weak Induction

With these sorts of fallacies, the problem is that the premises provide extremely weak support for the conclusion. They often disguise this fact by involving an emotional appeal of some sort.

1. Argument from Unqualified Authority:

Arguing for a conclusion based on the testimony of someone who is not qualified to speak on the relevant subject.

Example: Be careful and look out for lions when you go hunting next weekend; Dr. Lynch says that lions migrate south during the winter in the United States.

2. Appeal to Ignorance:

Drawing a conclusion based on a premise which states that nothing has been shown.

Example: No on has ever proven that ghosts don't exist. Therefore, they obviously do.

Note: There are some fairly common exceptions to this rule of thumb. Example: You have consistently failed to demonstrate your knowledge of the material on the exam. Therefore, I don't think you know the material.

3. Hasty Generalization:

A very bad inductive generalization.

Example: All three of the Ole Miss students I've met so far have been from Mississippi; so there must be no out-of-state students here.

4. False Cause:

Stating that there is a causal connection when one probably does not exist. There are different types (be sure to remember Slippery Slope):

Arguing from Coincidence: Example: When I've used my lucky pen before, I've passed the test; therefore I'll fail if I don't use that pen.

Oversimplifying the Cause: Example: Our society is filled with violence and there is a lot of violence on TV. It is obvious that the violence in society is caused by people watching television.

Slippery Slope: This is a very common variety of the false cause fallacy; it involves believing without any supporting reasons that X will lead to Y.

Example: Legalizing marijuana will lead to the legalization of cocaine. If you legalize cocaine, you'll be able to buy crack and every other drug at your local 7-11. In this argument, it is asserted that the legalization of marijuana will lead to (by degrees) the legalization of every drug. Once one accepts the legalization of marijuana, then one is assumed to be on the slippery slope towards the legalization of every drug.

Note: Sometimes slippery slope arguments are justifiable: for instance, if the reasons to accept x are just the same reasons that would lead you to accept y, then in accepting x, one should also accept y.

5. Weak Analogy:

Making a weak analogy, or unfairly comparing one thing to something else. It is very difficult to evaluate analogies with any degree of precision.

Example: Philosophy 101 is a philosophy class and has a lot of discussion; Logic is a philosophy class. So, it must also have a lot of discussion.

Here is an example of a false cause fallacy:

LUANN by Greg Evans


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