Logical Fallacies

Logical Fallacies Fallacies are statements that may sound reasonable or true but are deceptive and dishonest.

Ad Hominem (Personal Attack) Definition: This fallacy tries to divert attention from the facts of an argument by attacking the person making the argument. Example: The public should not take seriously Dr. Mason’s plan for upgrading county health services. He is a recovering alcoholic whose second wife recently divorced him. Why this shouldn’t be used: This attack on Dr. Mason’s character says nothing about the quality of his plan. Sometimes a connection exists between a person’s private lives – for example, in a case of conflict of interest. However, no evidence of such a connection is presented here.

False Dilemma Definition: This fallacy occurs when you suggest that only two alternatives exist even though there may be others. Example: We must choose between life and death, between intervention and genocide. There can be no neutral position on this issue. Why this shouldn’t be used: An argument like this oversimplifies issues and forces people to choose between extremes instead of exploring more moderate positions.

Red Herring Definition: This fallacy occurs when the focus of an argument is changed to divert the audience from the actual issue. Example: The mayor has proposed building a new baseball-only sports stadium. How can he even consider allocating millions of dollars to this scheme when so many professional baseball players are being paid high salaries? Why this shouldn’t be used: The focus of this argument should be the merits of the sports stadium. Instead, the writer shifts to the irrelevant issue of athletes’ high salaries

Misleading Statistics Definition: Although Statistics are a powerful form of factual evidence, they can be misrepresented or distorted in an attempt to influence an audience. Example: Women will never be competent firefighters; after all, 50% of the women in the city’s training program failed the exam. Why this shouldn’t use it: Here the writer neglected to mention that there were only two women in the program. Because this statistic is not based on a large enough sample, it cannot be used as evidence to support the argument.

Post Hoc, Ergo Propter Hoc Definition: This fallacy assumes that because two events occur close together in time, the first must be the cause of the second. Example: Every time a republican is elected president a recession follows. If we want to avoid another recession, we should elect a Democrat as our next President. Why this shouldn’t be used: Even if it were true that recessions always occur during the tenure of Republican presidents, or vice versa, no causal connection has been established. Correlation doesn't imply causation.

Non Sequiter Definition: This fallacy occurs when a statement does not logically follow from a previous statement. Example: Disarmament weakened the US after WW1. Disarmament also weakened the US after the Vietnam War. For this reason, efforts to control guns will weaken the US. Why this shouldn’t be used: The historical effects of disarmament have nothing to do with current efforts to control the sale of guns. Therefore, the conclusion is a non sequitur.

Begging the Question(Circular Logic) Definition: This is a fallacy that assumes, in the premise, what the arguer should be trying to prove in the conclusion. Example: The unfair and shortsighted legislation that limits free trade is clearly a wrong. Why this shouldn’t be used: Restrictions against free trade may be unfair and short sided, but “unfair” and “shortsighted” haven’t been proven.

Denying The Antecedent Definition: If P, then Q. Not P. Therefore, not Q. Example: If it's raining, then the streets are wet. It isn't raining. Therefore, the streets aren't wet. Why this shouldn’t be used: In this example, the street could have gotten wet from any number of things. While the street would be wet from rain, it doesn’t only get wet from rain.

Affirming the Consequent Definition: If P, then Q. Q. Therefore, P. Example: If a creature lives in the water to survive then it must be a fish. Dolphins live the water, so they must be fish. Why this shouldn’t be used: Even though dolphins live in the water like other fish, they are considered mammals because they breathe above water and give live birth.

False Analogy Definition: This fallacy is where perceived similarities are used as a basis to infer some further similarity that has yet to be observed.  Example: The overcrowded conditions in some parts of our city have forced people together like rats in a cage. Like rats, they will eventually turn on one another fighting and killing until a balance is restored. Why this shouldn’t be used: No evidence is offered that people behave like rats under these or any other conditions. Just because two things have some characteristics in common, you should not assume they are alike in other respects.