Philosophy 103 - Introduction to Logic: Critical Thinking

1/28 - Informal Fallacies


A fallacy is a mistake in an argument which consists in something other than merely false premises. A formal fallacy is simply an invalid deductive argument form. Informal fallacies, on the other hand, come in many different varieties.


Fallacies of Relevance

The conclusion is logically irrelevant to the premises, even if it is psychologically or emotionally relevant. They key to spotting a fallacy of relevance is to distinguish genuine evidence from emotional appeal.

1. Appeal to Force:

Arguing via threat: "I deserve a good grade, wouldn't you agree? If you don't agree, I'm afraid about what might happen: I just can't control Bruno here".

2. Appeal to Pity:

Trying to support a conclusion by evoking pity in the listener. I need to pass this class in order to graduate, if I don't graduate,, my parents will kill me. Therefore, I should receive a passing grade in the class".

3. Appeal to the People (argumentum ad populum):

Attempting to convince by appealing to the natural desire we all have to be included, or liked, or recognized. This type of fallacy breaks down into several sub-types.

Bandwagon: Of course God exists. Every real American believes that. Other related types: Appeal to Vanity; Appeal to Snobbery ("Of course you should cheat; all the cool people are doing it").

Note: In general, accepting a claim only because someone else believes it is a fallacy (not because you find them to be a credible source for instance . . .). So, we could say that another example of an ad populum is:

Appeal to Belief. Example: "90% of those surveyed think we should not convict Clinton, so you should too".

Closely related is the

Appeal to Common Practice. Example: "Hey, everyone speeds. So speeding isn't wrong".

4. Argument against the Person (Ad hominem):

Attacking the source of an argument instead of the argument itself. This also comes in several varieties:

Abusive: Lynch says that we should spend more state revenue on education because doing so would result in a more productive workforce. But lynch is a bleeding-heart, liberal Yankee from New York -- so you know that his opinion is worthless.

Circumstantial: Lynch says that we should spend more state revenue on education. But Lynch is a professor who wants a better salary -- so you know that his opinion is worthless.

From Hypocrisy: You've claimed that smoking is bad for one's health; but you smoke too.

Notice: if a person with low credibility asserts something without supplying evidence for it, then we should withhold judgment. But, if the person does supply reason for the claim, then we still need to look at those reasons and evaluate whether they support the conclusion in question.

Another thing to be aware of is convicting someone of holding contradictory beliefs. If we can show this, then we have indeed supplied a good reason to believe that the person is confused. But notice that people can change their minds. Changing your mind is fine; contradictory beliefs are not.

5. Accident:

Applying a general rule to a case it was not designed to cover. Example: Killing is bad: therefore, it was wrong for us to go to war against the Nazi's.

6. Straw Man:

Attacking an oversimplified version of an opponent's actual position. Example: Those who support gun control are wrong; they believe that no one should has the right to defend themselves in any situation.

7. Missing the Point/Red Herring:

Two closely related fallacies, which involves diverting the listener's attention by changing the subject or drawing a slightly different conclusion than the one that should be drawn. Example: The death penalty is the only way to punish criminals. Why? Because the justice system in this country has gone straight to hell -- what with murderers, rapists and robbers getting off scot-free! It has got change!

Study Break: Argument 101 - a humorous look at how to win an argument.