Fallacies in public speaking

Formal Fallacy Formal fallacies occur when there is a problem with the form, or structure, of the argument. "Formal" refers to the form of the argument. An argument that contains a formal fallacy will always be invalid.

Informal Fallacies An informal fallacy is an error in reasoning that occurs due to a problem with the content, rather than mere structure, of the argument. In informal logic and rhetoric, a fallacy is usually an error in reasoning often due to a misconception or a presumption. Some of the more frequent common logical fallacies are:

Hasty Generalization Argues from limited examples or a special case to a general rule. Argument: Every person I've met has ten fingers, therefore, all people have ten fingers. Problem: Those, who have been met are not a sufficient representative subset of the entire set.

Argumentum ad hominem Making the argument personal attacking or discrediting the opposition's character Argument: What do you know about the U.S? You aren't even a citizen. Problem: personal argument against an opponent, instead of against the opponent's argument.

Bandwagon (argumentum ad pupulum) an appeal to the majority; appeal to loyalty Argument: Everyone is doing it. Problem: Concludes a proposition to be true because many or most people believe it.

Red Herring Intentionally or unintentionally misleading or distracting from the actual issue. Argument: I think that we should make the academic requirements stricter for students. I recommend that you support this because we are in a budget crisis and we do not want our salaries affected. Problem: Here the second sentence, though used to support the first, does not address the topic of the first sentence, instead switching the focus to the quite different topic.

Non sequitur Fallacy of false cause Incorrectly assumes one thing is the cause of another. Non Sequitur is Latin for "It does not follow." Argument: I hear the rain falling outside my window; therefore, the sun is not shining. Problem: The conclusion is false because the sun can shine while it is raining.

Post hoc ergo propter hoc If it comes before it is the cause believing that temporal succession implies a causal relation. Argument: It rained just before the car died. The rain caused the car to break down. Problem: There may be no connection between the two events.

Cum hoc ergo propter hoc Two events co-occurring is not causation Believing that correlation implies a causal relation. Argument: More cows die in the summer. More ice cream is consumed in summer months. Therefore, the consumption of ice cream in the summer is killing cows. Problem: No premise suggests the ice cream consumption is causing the deaths. The deaths and consumption could be unrelated, or something else could be causing both, such as summer heat.

Loaded questions Groups more than one question in the form of a single question. Argument: Have you stopped beating your wife? Problem: Either a yes or no answer is an admission of guilt to beating your wife.

Straw man Creates the illusion of having refuted a proposition by replacing it with a superficially similar proposition (the "straw man"), and refuting it, without ever actually refuting the original. Argument: Person A: Sunny days are good Person B: If all days were sunny, we'd never have rain, and without rain, we'd have famine and death. Therefore, you are wrong. Problem: B has misrepresented A's claim by falsely suggesting that A claimed that only sunny days are good, and then B refuted the misrepresented version of the claim, rather than refuting A's original assertion.

False dilemma (either-or) The listener is forced to make a choice between two things which are not really related or relevant. Argument: If you are not with us, you are against us. Problem: The presentation of a false choice often reflects a deliberate attempt to eliminate any middle ground.

Card-Stacking Deliberate action is taken to bias an argument by selective use of facts with opposing evidence being buried or discredited. Argument: Learn new skills, become a leader and see the world. Problem: Only the positive benefits of military service are used to recruit , and not the hazards.

Slippery Slope This is a conclusion based on the premise that if A happens, then eventually through a series of small steps, through B, C,..., X, Y, Z will happen, too, basically equating A and Z. So, if we don't want Z to occur, A must not be allowed to occur either Argument: If we ban Hummers because they are bad for the environment eventually the government will ban all cars, so we should not ban Hummers. Problem: In this example, the author is equating banning Hummers with banning all cars, which is not the same thing.

Circular Argument This restates the argument rather than actually proving it. Argument: George Bush is a good communicator because he speaks effectively. Problem: the conclusion that Bush is a "good communicator" and the evidence used to prove it "he speaks effectively" are basically the same idea. Specific evidence such as using everyday language, breaking down complex problems, or illustrating his points with humorous stories would be needed to prove either half of the sentence.

Begging the Claim The conclusion that the writer should prove is validated within the claim. Argument: Filthy and polluting coal should be banned. Problem: Arguing that coal pollutes the earth and thus should be banned would be logical. But the very conclusion that should be proved, that coal causes enough pollution to warrant banning its use, is already assumed in the claim by referring to it as "filthy and polluting."

Moral Equivalence This fallacy compares minor misdeeds with major atrocities. Argument: That parking attendant who gave me a ticket is as bad as Hitler. Problem: In this example, the author is comparing the relatively harmless actions of a person doing their job with the horrific actions of Hitler. This comparison is unfair and inaccurate.

Genetic Fallacy Genetic Fallacy: Rejecting an argument based on its origins rather than on its own merits. A related form accepts or rejects arguments based on others who endorse or reject those same arguments. Argument: You think labor unions are good? You know who else liked labor unions? Karl Marx, that’s who. Problem: The argument rejects labor unions on the grounds that Marx liked

Syllogism an instance of a form of reasoning in which a conclusion is drawn (whether validly or not) from two given or assumed propositions (premises), each of which shares a term with the conclusion, and shares a common or middle term not present in the conclusion Deductive reasoning is a logical process in which a conclusion is based on the concordance of multiple premises that are generally assumed to be true.  Deductive reasoning is sometimes referred to as top-down logic. Its counterpart

The Example All flowers are animals. All animals can jump. Therefore, all flowers can jump. Even though it is quite obvious that the first premise is not true and further that the conclusion is not true, the whole syllogism is still valid. By applying formal logic to the syllogism in the example, the conclusion is still valid.

Undistributed Middle An argument in which the middle term is undistributed, meaning that not all the instances of things that are C are also instances of things that are A or of B. In other words, the first premise tells us that everything that is an A is also a C. It doesn’t tell us anything about whether things that are C are also things that are A. Similarly, in the second premise, we are told that everything that is a B is also a C. But again, we know nothing about things that are C. A is a C. B is a C. Therefore A is a B. The argument is seductive because of its surface similarity to a valid argument form: A is a C. C is a B. Therefore A is a B In this argument, we know something about A (namely, that every instance of A is also an instance of C). And we also know something about C (namely, every instance of C is also an instance of B). Since the C is distributed in the second premise, we can correctly link A with B. Argument: Most Arabs are Muslims and all the 9/11 hijackers were also Muslims. Therefore most Arabs are hijackers. Problem: The conclusion doesn’t follow from the premises. To show this, substitute the following argument: My 5-year-old enjoys watching television, and teenagers also enjoy watching television. Therefore my 5-year-old is a teenager.

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