It’s hard to imagine having a proper debate without knowledge of logical fallacies. For one thing, they’re just so common. If you want to argue better, or be better able to discriminate between sides of an argument, you’re in the right place. Just remember to flavor your powers of logic with tact.
Here’s how to analyze an argument for soundness: First, notice whether or not the form of the argument makes sense. Does the conclusion follow from the premises? If not, you likely have a formal fallacy on your hands. As a beginning logician, don’t spend too much time figuring out the name of the fallacy; instead, point out the problem and say something like, “The conclusion doesn’t follow the premises.” Step two is to notice whether or not the statements made in the argument are true; if not, there is an informal fallacy. You should be able to identify all ad hominem fallacies and name them as such. You should also be able to call out these fallacies by name: the fallacy of equivocation; the slippery slope fallacy; the poisoning the well fallacy; the straw man fallacy; the appeals to emotion, fear, pity, ridicule and the like; and the appeals to tradition, authority, and popularity. Other fallacies can simply be identified as a logical fallacy, and often, this is enough.
Important note: Many logical fallacies are known by more than one name. I’ve attempted to use the most common in my list, but if you rely too much on memorization, you won’t always recognize other people’s terms. More important, you’ll miss the point.
Finally, a quote to consider by Gongsun Long, a Chinese logician of ancient times: “One and one cannot become two, since neither becomes two.”
I think that pretty much says it all.
ESSENTIAL KNOWLEDGE: LOGIC AND RHETORIC
Logic: The set of rules for forming valid arguments; the study of rational argumentation. The word comes from the Greek word logos, originally meaning “the word,” “thought” or “reason.”
Rhetoric: The art of persuasion through the use of language
Semantics: The study of word meanings and usages, which can be complicated by cultural and linguistic factors
Argument: A set of statements that supports an opinion or position. A logical argument attempts to demonstrate the factual accuracy of a position and is usually expressed as two or more premises that lead to a conclusion. An example is: “All A’s are B’s and all B’s are C’s; therefore, all A’s are C’s.” A rhetorical argument attempts to persuade someone of a position, whether or not the position is factually accurate.
Valid: Containing a conclusion that logically follows from the premises. An example is: “All men are mortal. Socrates is a man. Therefore, Socrates is mortal.”
True: Accurate and corresponding with reality
Rational: Both logically valid and factually accurate; sound. An example is: “All zebras are mammals and all mammals have fur; therefore, all zebras have fur.”
Premise: A statement that forms the basis of an argument and leads to a conclusion. When it is false, the conclusion might also be false. In the argument “All A’s are B’s and all B’s are C’s; therefore, all A’s are C’s,” the two premises are “All A’s are B’s” and “All B’s are C’s.”
Antecedent: The part of an argument that comes before the “if.” In the premise “If A, then B,” A is the antecedent.
Consequent: The part of an argument that comes after the “then.” In the premise “If A, then B,” B is the consequent.
Deductive reasoning: Drawing a specific conclusion based on a general principle. An example is: “All zebras are mammals, and all mammals have fur; therefore, zebras have fur.”
Inductive reasoning: Arriving at a general principle based on specific facts or observations. An example is: “All apples I have ever eaten are sweet; therefore, all animals are sweet.”
Analysis: Pulling apart an argument to describe its individual elements
Synthesis: Putting the parts of an argument together to find its overall meaning
A priori: Known to be valid or true by reason alone. It means “from the earlier” in Latin.
A posteriori: Known to be valid or true through observation and experience, not reason. It means “from the latter” in Latin.
Logical fallacy: A weakness in an argument, often hidden, that leads to an invalid conclusion
Formal logical fallacy: A fallacy in the structure of the argument that causes the argument to be invalid or illogical, regardless of the factual accuracy of its conclusion. There are many types of these, and they often take the form of either affirming or denying the antecedent or the consequent. An example is the denying the consequent fallacy, which follows the form, “If A, then B; not B, therefore not A,” as in, “If Fred killed Todd, then he hated him. Fred didn’t hate Todd. Therefore, he didn’t kill him.”
Informal logical fallacy: A fallacy in the content of the argument that causes the argument to be invalid or illogical, regardless of the factual accuracy of its conclusion. There are many types of these, and many of these are simple distractions from the actual argument.
Ad hominem fallacy: A fallacy in which the arguer points to someone’s character, background or other characteristics, rather than to the relevant facts. The name comes from the Latin phrase meaning “against the person.” An example is: “Jane has a felony record so she won’t be a good student.”
Appeal to authority fallacy: A fallacy in which the arguer points to someone’s knowledge, training or other credentials, rather than to the relevant facts. An example is: “My professor told me this, so it must be true.”
Equivocation fallacy: A fallacy in which the arguer uses multiple definitions of the same word, misleading the audience. An example is: “I have a right to bear arms. Therefore, it is right for me to bear arms.”
Straw man fallacy: A fallacy in which the arguer misrepresents the opponent’s position as being weaker than it really is. An example is: “The opponent is saying that they want extremely high taxes for everyone, even people who cannot afford it.”
Slippery slope fallacy: A fallacy in which the arguer claims that a relatively small first step leads necessarily to a chain of related events, which it might or might not do. An example is: “If gay marriage becomes legal, people will soon start marrying animals.”
Poisoning the well fallacy: A fallacy in which the arguer presents adverse information about an opponent with the intention of discrediting everything the opponent says. An example is: “The candidate is a liar and a cheat.”
Appeal to emotion fallacy: A fallacy in which the arguer attempts to manipulate an audience’s emotions. This is a general category that includes the appeal to threat fallacy, the appeal to fear fallacy, the appeal to flattery fallacy, the appeal to pity fallacy, the appeal to ridicule fallacy and more. An example is: “If you change careers, it will disappoint your family.”
False dilemma fallacy: A fallacy in which the arguer presents a limited number of options (usually two), implying these are the only options possible, when in reality there are more. An example is: “Either you like apples or you don’t. If you like them, you should eat them every day, and if you don’t, you should never eat them.”
Begging the question fallacy: A fallacy in which the arguer states the conclusion as part of the premise in order to make the argument appear logical. An example is: “God exists because the Bible says so, and the Bible is the word of God.”
Ad nauseam fallacy: A fallacy in which an arguer relies on mere repetition. The name comes from the Latin phrase meaning “to the point of nausea.”
Ad infinitum fallacy: A fallacy in which the arguer doesn’t directly lead to a conclusion and instead, merely adds additional facts and information. The name comes from the Latin phrase meaning “to infinity.”
Non sequitur fallacy: A fallacy in which the arguer draws a conclusion that does not logically follow from the premises or evidence presented. The name comes from the Latin phrase meaning “it does not follow.” An example is: “All dogs are animals. My cat is not a dog. Therefore, my cat is not an animal.”
Appeal to tradition fallacy: A fallacy in which the arguer relies on long-held truths rather than the relevant facts. An example is: “We have always gone to church on Sundays. Therefore, Sunday is the best day to go to church.”
Appeal to the people/bandwagon fallacy: A fallacy in which the arguer claims a position to be true or good solely because a majority or many people believe it to be so. An example is: “This is the top brand of toothpaste. Therefore, it must be good.”
Guilt by association fallacy: A fallacy in which the arguer assumes that something related to something bad is also bad. An example is: “Tom is friends with Sarah, and Sarah spent time in jail. Therefore, Tom can’t be trusted.”
Honor by association fallacy: A fallacy in which the arguer assumes that something related to something good is also good. An example is: “Tom is friends with Sarah, and Sarah is an engineer. Therefore, Tom knows about engineering and her opinion can be trusted.”
Red herring fallacy: A fallacy in which the arguer attempts to distract an audience by deviating from the topic at hand by introducing a separate argument the speaker believes is easier to speak to. An example is: “We shouldn’t invest in education. We should focus on reducing crime instead.”
Cherry picking fallacy: A fallacy in which the arguer selects individual cases or data points that seem to confirm their position, while ignoring other, contradictory cases or data points. An example is: “We have many positive reviews of our product, so it must be good.”
Appeal to consequences fallacy: A fallacy in which the arguer describes the consequences of a position, rather than whether or not the position is true. An example is: “If they pass the law, people will get more divorces. Therefore, we shouldn’t pass the law.”
Appeal to motive fallacy: A fallacy in which the arguer attacks the motives of the opponent. An example is: “Sarah works for the company that she is advocating for. Therefore, she can’t be trusted.”
Tu quoque fallacy: A fallacy in which the arguer points out the hypocrisy of the opponent. The name comes from the Latin phrase meaning “you too.” An example is: “You drive a car, so your opinion about carbon emission reduction isn’t reliable.”
Etymological fallacy: A fallacy in which the arguer uses the historical, disused meaning of a word or phrase as a way to support an argument. An example is: “I am gay, so that must mean I’m happy.”
Moving the goal posts/raising the bar fallacy: A fallacy in which the arguer dismisses the opponent’s evidence and demands additional, harder-to-find evidence. An example is: “I won’t believe the results unless I can see ten more DNA test results.”
Survivorship bias fallacy: A fallacy in which the arguer points to a small number of successes while ignoring a large number of failures. An example is: “I am great at choosing stock because of the three times I chose correctly.”
False analogy fallacy: A fallacy in which the arguer presents an analogy that does not suit the situation or conclusion. An example is: “Running the economy is like running a small business and the same strategies apply to both.”
Hasty generalization: A fallacy in which the arguer draws a broad conclusion based on a small sample or on an example that might not represent the whole. An example is: “This cat scratched me, so all cats must be bad-tempered.”
Oversimplification fallacy: A fallacy in which the arguer assumes that there is one, simple cause of an outcome when in reality there might have been more than one. An example is: “Poverty can be solved if people just worked harder.”
Appeal to ignorance: A fallacy in which the arguer assumes that a claim is true because it has not been or cannot be proven false, or vice versa. An example is: “Aliens must exist because we have no evidence that they don’t.”
Pooh-pooh fallacy: A fallacy in which the arguer deems the opponent’s position as unworthy of serious consideration. An example is: “The idea that global warming affects ocean temperature is ridiculous. Therefore, it can’t be true.”
Moralistic fallacy: A fallacy in which the arguer assumes that what ought to be true, is in fact true. An example is: “Lying is always wrong, so this lie is also unjustifiable.”
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