Fallacies are errors in reasoning (deliberate or not) that weaken an argument and, of course, the quality of the essay that contains the argument. Fallacious arguments seem dishonest whether or not the writer intended them to be. While fallacies may sound logical, they are far from it. To avoid using logical fallacies you must be able to understand and identify logical fallacies, so let’s take a look at the following list of common fallacies, with examples.
HASTY GENERALIZATIONS
Hasty generalizations are committed when a person draws a conclusion about a population based on a sample that is not large enough. A hasty generalization usually rests behind a stereotype–that is, a person or event is treated as typical of a whole class. For example, while it may be true that, based on your personal experience, that the only native Russians you know personally do not speak English fluently, that is no basis for asserting that all Russians do not speak English fluently.
Example of a Hasty Generalization
- Thomas failed at his first attempt to fix my computer network. Computer programmers usually don’t know what they’re doing.
Rationale for Why This Logical Fallacy Should be Avoided
Give Thomas another chance or two before condemning him and the whole profession of computer programming. One piece of evidence against one person is not enough to support a generalization about an entire profession.
AD HOMINEM (PERSONAL ATTACK OR NAME CALLING)
“Ad Hominem” is Latin for “against the man” or “against the person.” This fallacy is committed when an argument is rejected on the basis of some irrelevant fact (a personal attack or name calling, most often) about the person presenting that argument.
Example of an Ad Hominem attack
Senator Johnson’s new tax bill has some good points, but I oppose it. Johnson has been divorced five times, and he may be charged with fraud in the future.
Rationale for Why This Logical Fallacy Should be Avoided
How does Johnson’s personal life relate to his tax legislation? Sometimes, imperfect people have innovative ideas that may be worth considering. Moreover, personal attacks and name calling distract from the topic or issue at hand.
FALSE AUTHORITY (ERRONEOUS APPEAL TO AUTHORITY)
This fallacy is committed when an argument depends on an authoritative person, who is truly not an expert on the issue in dispute. The fact that a high-energy physicist won the Nobel Prize is no reason to attach any special weight to their views on the causes of cancer or the legalization of marijuana.
Example of False Authority
“I’m not a doctor but I play one on T.V. Use this aspirin.”
Rationale for Why This Logical Fallacy Should be Avoided
- How can an acclaimed actor be an expert on aspirin? Simply because someone is famous or “plays a doctor on TV” does not make that person credible or qualified to speak about a topic or idea they have no direct experience with, especially if said actor is being paid to endorse a product or stance.
This fallacy can be corrected if it satisfies the following:
- The claim being made by the person is within their area(s) of expertise.
- There is an adequate degree of agreement among the other experts in the subject in question.
- The person in question is not significantly biased.
- The area of expertise is a legitimate area or discipline.
SLIPPERY SLOPE
This argument claims that one event, action or idea will inevitably lead to another, usually with terrible consequences. Often we encounter this mode of argument in the public debates over handgun control, censorship, etc. This fallacy implies that the first step necessarily leads to the second, and so on down the slope to disaster.
Example of a Slippery-Slope Argument
- If we let students wear T-shirts with obscene messages on them, the next thing we know, they’ll be smoking marijuana behind the gymnasium.
- “We have to stop the tuition increase! The next thing you know, they’ll be charging $40,000 a semester!”
Rationale for Why This Logical Fallacy Should be Avoided
- Someone who puts forth a slippery slope claim sees one change as inexorably leading to a more drastic, horrible change when, in fact, the two events may be unrelated, or one event may not necessarily have a catastrophic result.
CIRCULAR REASONING (BEGGING THE QUESTION)
This fallacy attempts to support a statement by simply repeating the statement in different or stronger terms. In this fallacy, the reason given is nothing more than a restatement of the conclusion that poses as the reason for the conclusion.
Example of Circular Reasoning
- Barak Obama is a good communicator because he speaks effectively.
Rationale for Why This Logical Fallacy Should be Avoided
- Notice how the writer draws a conclusion from the assumption they have already made. The writer claims “Barak Obama is a good communicator”; yet, their reason to support that claim is that “he speaks effectively”. Isn’t the writer’s reason the very same claim that they are making? Therefore, the writer needs to explain and prove what makes Barak Obama an effective speaker and a good communicator.
EITHER-OR SIMPLIFICATION (FALSE DICHOTOMY)
Either-or arguments falsely claim that there are two sides of an argument or two possible outcomes. This type of argument is also known as a false dichotomy.
Example of an Either-or Simplification
- We should build the new house using an original plan, or we shouldn’t build it at all.
Rationale for Why This Logical Fallacy Should be Avoided
- Such a pair of choices leaves no room for other options. The dilemma presented is a false one because there almost always are more than two options in any given situation.
For more examples of logical fallacies used in argument, refer to the Purdue Global Writing Center resource on How to Support an Argument and Avoid Logical Fallacies.