6. Informal Fallacies in Reasoning




Logic may well have begun, historically, when people first noticed that there are patterns or approaches to reasoning that cannot be trusted. In Plato’s dialogues, you often see references to people who “make the weaker argument appear the stronger,” i.e., people who manipulate language so skillfully that they can convince others of things that they should not really be convinced of.

More precisely, Logic is more concerned with the process or the pattern of reasoning than it is with the thing believed: Logic is concerned with whether the reasoning is good or not, but a given belief might be better supported by one argument than by another.

For instance, I think it’s a good idea that we all believe that killing others is wrong. But the following reasoning for it is not one we can endorse: “Killing is wrong because if you kill someone you’ll go to Hell.”

That argument is a good example of a fallacy that has been known as the Appeal to Force (or the Appeal to the Stick) at least since Aristotle’s time. The fallacy lies in invoking the threat of harm as evidence that some statement is true (or false). That makes no more sense as an argument for the conclusion than if I said “The Earth is flat, and if you don’t agree, my friend here is going to break your legs for you.” The two things have, literally, nothing to do with each other. If something is true, it is true regardless of who is going to get hurt or get a happy meal.

We use the word “fallacy” in Logic to refer to a bad argument or a mistake in a piece of reasoning. A certain number of fairly common recurring patterns of such mistakes have become well-known over the centuries, and they will be the topic of this chapter.

In everyday life, “Fallacy” is often used in a slightly different sense, to mean a mistaken belief (e.g., one might hear a misanthrope speak of the fallacy of trusting everyone you meet). If these two meanings of the word have a connection other than sloppiness, it is probably the inclination we spontaneously have of thinking that bad arguments will lead to false statements or conclusions. But as we saw in the chapter on the difference between induction and deduction, this is by no means necessarily true. It is quite possible for a weak inductive argument to have a true conclusion, and it is quite possible for an invalid deductive argument to have one as well. In those cases, the truth of the conclusions is not established by the argument in question, but is independent of it. Take a few minutes to refresh your understanding of this, by generating a simple example of a weak argument with a true conclusion, and a simple example of an invalid one with a true conclusion.


A simple way to understand what the fallacies we’re going to be talking about are is to think of them as attractive patterns of sloppy or bad reasoning. By “attractive” what I mean is that people fall for them, both as arguers and as listeners. For a variety of reasons, it is fairly easy to go along with or be taken in by these patterns or approaches. If you do a quick Google search on the Web for fallacies, you’ll find dozens and dozens, and you’ll see that different sites make different choices about how to categorize them. This might make you wonder why logicians just can’t get their act together. But the real moral is: there is something inherently sloppy about sloppy reasoning, and that extends to the attempt to nail it down with clarity!


For this course, we are going to set ourselves the task of learning twenty-one fallacies. By “learn,” I mean you are going to commit these twenty-one names to memory, and be able to explicate each of them as well as identify them when they occur in passages.

I’ll follow a pretty standard approach to grouping them into four sets:




As used in logic, the word “fallacy” means a defective or unreliable pattern of reasoning, not a mistaken belief (as it often means in daily life situations). The following list of 21 fallacies is broken down into four “families.

I. Fallacies of Relevance

1. Appeal to the People. The attempt to prove that something is true on the grounds that others/”everyone”/ “they” say so. It’s called “direct” when you (the listener) are spoken to as a member of the people (as in “We Americans are not going to let ourselves be dictated to by others, so it is time to dismantle the U.N.”) and it’s called “indirect” when you are spoken to as a potential outsider (e.g., “If you want everybody to laugh at you, sure, go ahead and sign up for that course on feminism”).

Perhaps more convincing: imagine it’s the year 1066 and someone says “Of course the world is flat, everyone knows that!”  His premise is true (although they really think they know it, it’s their opinion –you can’t really know something if that thing is false); does that mean his conclusion is true?  It is possible for everyone to believe something and for them to all be mistaken!  So by itself, universal approval of an opinion is not evidence of its truth.

2. Appeal to Pity. The attempt to prove that something is true by making your listener feel bad in some manner. E.g., Smith’s girlfriend just died, so he should get a raise.

3. Appeal to Force. The attempt to prove that something is true by invoking a threat. E.g., Stealing is wrong, because if you do it you’ll go to Hell.

4. Attack on the Person (ad hominem). The attempt to disprove another person’s argument by attacking the person’s character, circumstances or consistency. E.g., Andy is a loser, so his argument against gun control is worthless.  This attacks his character. Or: Billy argues that gun ownership is everyone’s right, but what do you expect, he owns a sporting goods store. This attacks his circumstances, not his characater.  Or: Gov. Spitzer got elected arguing that we need to crack down on organized prostitution, but it turns out he spent thousands visiting prostitutes himself, so there mustn’t be anything wrong with it after all.  This attacks Spitzer as a hypocrite.

It’s important not to go overboard with this kind of critique. It is not a logical fallacy to call a person of bad character out on his or her character, and it is not a logical fallacy to call a person a hypocrite. The fallacy lies in claiming to show that someone’s argument is no good, and as evidence, pointing to some such flaw.  But an argument’s conclusion is not dependent on the person who makes it.  If Hitler or Stalin made the argument that “Socrates is a man and all men are mortal, so Socrates is mortal,” the argument would be just as valid as if Jesus or Gandhi made it. An argument is valid or not, or strong or not, depending on whether or not the premises –statements–support the conclusion; the goodness of an argument is not a function of the goodness of the person who makes it. The fallacy is thinking that it is and arguing on that basis!

5. Straw Person. The attempt to disprove another person’s argument by summarizing it in a way that distorts it, and attacking the distorted version. E.g., The Democrats are all gung-ho for universal healthcare this time around. But McCain has his head on right: we don’t need communism in the USA.

Here are a few more examples:

**John: Sunny days are the best! Paul: If all days were sunny, we’d never have rain, and without rain, we’d have famine and death.    [Comment: John did not offer an argument, just an opinion, so Paul is not really aiming to refute his argument, but he does seem to offer an exaggeration of John’s point.]

** When campaigning for vice president in 1952, Nixon was accused of having illegally appropriated $18,000 in campaign funds for his personal use. In a televised response, instead of addressing the funds, he spoke about another gift, a dog he had been given by a supporter:[12][13] It was a little cocker spaniel dog, in a crate he had sent all the way from Texas, black and white, spotted, and our little girl Tricia, six years old, named it Checkers. And, you know, the kids, like all kids, loved the dog, and I just want to say this right now, that, regardless of what they say about it, we are going to keep it.

[Comment: This was a straw man response; his critics had never criticized the dog as a gift or suggested he return it. This argument was successful at distracting people from the funds, and portraying his critics as nitpicking and heartless. Nixon received an outpouring of public support, remained on the ticket, and was elected by a landslide.  (From Wikipedia)]

** From a draft of a bill (HCR 74) considered by the Louisiana State Legislature in 2001:[7] Whereas, the writings of Charles Darwin, the father of evolution, promoted the justification of racism, and his books On the Origin of Species and The Descent of Man postulate a hierarchy of superior and inferior races. . . . Therefore, be it resolved that the legislature of Louisiana does hereby deplore all instances and all ideologies of racism, does hereby reject the core concepts of Darwinist ideology that certain races and classes of humans are inherently superior to others, and does hereby condemn the extent to which these philosophies have been used to justify and approve racist practices.

[Tindale comments that “the portrait painted of Darwinian ideology is a caricature, one not borne out by any objective survey of the works cited. That similar misrepresentations of Darwinian thinking have been used to justify and approve racist practices is beside the point: the position that the legislation is attacking and dismissing is a Straw Man. (from Wikipedia)]

6. Red Herring. The attempt to disprove another person’s argument by changing the subject to something you present as “the real issue.” E.g., Animals rights activists complain that biomedical research laboratories torture and abuse animals. But what about this: pet owners abuse and beat their pets all over this country every single day. In fact, some studies say that as many as 25% of pet owners kick or beat them on a regular basis –it’s enough to make you sick.

Here are a few more examples, found by students reporting on fallacies for this class:

* “I can’t agree with those who argue for the right for homosexuals to marry. Anyway, taxes on married people are high. I think that taxes on the married are just ridiculous.”

* Reporter: “It seems to me that if you were elected president, the Congress with which you would have to work would not be very cooperative at all. How could you, as president, bring about any reform or help enact any beneficial legislation with a Congress that was almost totally opposed to your programs?” Ross Perot: “Well, if I were elected, about half the members of Congress would drop dead of heart attacks, and half of my problem would be solved from the outset.”

* “While you may have concerns about my votes about the environment, I can assure you that I am an open minded individual. What we should really discuss is my record on votes that expanded educational opportunities for all children.”

* “I am pretty sure that evolution is not a very good explanation for human life. Anyway, I am pretty offended that anyone would suggest that I came from a monkey.”

I hope you wonder why fallacies of relevance are called “fallacies of relevance.” It’s about the kind of relevance their premises have for their conclusions. They fail to be logically relevant to the conclusions, but it should be very obvious that they are psychologically quite relevant. That is, the threat of harm, the feeling of pity, the shame of being called a name, or being left out, etc., are strong motivations for people to accept what others tell them to accept. And they are all logically irrelevant.

You should learn the Latin name “Ad Hominem” for the Attack on the Person; it is a commonplace.

II. Fallacies of Weak Induction

7. Hasty Generalization. Basing a generalization on too little evidence (too few examples) or unrepresentative evidence. E.g., Birds are incredibly stupid animals; one of them just flew into my window and killed itself.

A few more provided by students in 2015:

*Dogs are incredibly vicious animals; one of them bit me for reaching out to pet it.

*Elena smoked and drank everyday from the age of fifteen until she was eighty years old. Therefore smoking and drinking can’t be bad that you.

*My Christian neighbor is a really mean man. Therefore Christians are mean.

*Chris is skinny and eats six bags of chips everyday. Therefore, eating six bags of chips won’t make you fat.

8. Accident. Applying a general rule to an exceptional circumstance, or mistaking what is accidental (non-essential) for what is essential. E.g., This school has a strict drug-free policy, so you can’t bring that triple espresso into the office, because caffeine is a drug.

Or: Lying is wrong, so you will have to tell Joe where his estranged wife is hiding if he asks.

Or: You reap what you sow, and the corn you planted cost you 50 cents a bushel, so that’s what you’ll have to sell it for.

Student contributions from the web:

1. Drinking and driving is unsafe, so you shouldn’t bring your Pepsi in the car.

2. Taking something that is not yours is stealing, so the child picking up a penny off the street should be arrested.

3. Assault is a crime so all Professional Boxers should be arrested.

4. Speeding is dangerous so all EMTs responding to calls must strictly obey speed limits.

5. Causing someone pain is wrong, so all surgeons are bad people.

9. False Cause. Arguing that one thing is the cause (or effect) of another on the basis of mere temporal succession or mere correlation/ coincidence. E.g., Ronald Reagan defeated communism because he said “Mr. Gorbochev, tear down this wall,” and the Berlin Wall was down within a year. Or:  I prayed that the Patriots would win the Super Bowl, and they did!  God heard my prayer.

10. Slippery Slope. Arguing for likely catastrophic consequences as a result of a chain reaction that one “first step” will supposedly (but unlikely) set off. E.g., Euthanasia is completely intolerable, because once you allow for mercy killings of sick old people, then next it’ll be sick poor people, and then sick homeless people, and pretty soon anyone who’s got a serious flu will be targeted.

The following link should take you to an April 20, 2015 Washington Post column about an argument being made against same-sex marriage; an excellent example of the slippery slope fallacy:   http://www.washingtonpost.com/opinions/the-new-argument-against-gay-equality-same-sex-marriage-kills/2015/04/20/9fc509d4-e7a3-11e4-aae1-d642717d8afa_story.html  

11.Weak Analogy. Basing a conclusion on a similarity between things when the similarity is not relevant. E.g., The Smith’s home and the Jones’ home are both on the same street and were built in the same year, so they probably cost the same.

Or: Your 1999 Cadillac and my 2011 Prius are both silver, and my Prius gets 35 miles to the gallon, so your Cadillac probably gets 35 miles to the gallon too.

The following analogies were proposed as examples by students who did a web search on Weak analogy.  My response in each case is that these are only comparisons or analogies, but no conclusion is proposed to follow from them.

Guns are like hammers, they are both made from metal and can be used for murder.

A horse is like a dog, they both can swim.

Humans are like cats because they are mammals and warm-blooded.

A private college is like a public college, they both have dorms.

If one proposed, from the first, that therefore guns should not be regulated, since hammers are not, it would be the fallacy we’re discussing here. If one proposed, from the second, that it is possible to ride on dogs, it would be the fallacy. If one proposed, from the third, that humans can clean their entire bodies with their own tongues…

If one proposed, from the fourth, that private colleges are just as affordable as public ones…

But, until some conclusion is based on the analogy, it is only an analogy, not a fallacy.


12. Appeal to Ignorance. Concluding that something is true because it has not been proven false (or vice versa). E.g., There is insufficient evidence to prove that Martins is the perpetrator, therefore he did not commit the crime. (Note the difference between that and this non-fallacious conclusion: There is insufficient evidence to prove that Martins is the perpetrator, therefore we find him ‘not guilty’ before the law.) Two more examples provided in a student report:

* She hasn’t said she doesn’t like you, right? So she’s probably interested. Call her up.

* No one has seen what Spider-Man looks like under his costume, so he must be a spider.

13. Appeal to Authority. Arguing that something is true because someone else has said so, but when the supposed authority or expert really lacks the relevant expertise, or can be suspected to have a bias. E.g., women should not have the vote, after all, Aristotle said their souls lack the deliberative faculty.

Or: Deductive arguments are every bit as good as inductive ones because I asked my mom, and she said so.


It should be clear, from knowing the six kinds of typical inductive patterns of argument, that each of them is susceptible to its weakness. The one that is new here is the Appeal to Ignorance. The word “ignorance” has to be taken in the specific sense of “a lack of knowledge,” not in the everyday sense of “stupidity” or “foolishness.” If there is no evidence for x, then nothing can be concluded about x. Concluding something from a lack of evidence is the fallacy.

III. Fallacies of Presumption

14. Begging the Question (petitio principi). Drawing a conclusion from premises that presuppose something which ought to be addressed but isn’t. Arguing in a circle is another form of this, as is restating the premise as the conclusion in different words. E.g., Abortion is wrong because murder is wrong.    (“Is abortion murder?” is the question that is skipped over here.) Or: we have the right to control our own bodies, so abortion cannot be regulated. (“Is the fetus just another body part?” is the question that is skipped over here.) Or: Cervantes is the greatest author to ever live because no one is better than him.

15. False Dichotomy. Drawing a conclusion from a false “either…or” statement, which presents a choice as exhaustive when it is not really. E.g., Either you vote for Romney or the war in Afghanistan will go on for another hundred years. You don’t want that, do you? So…

Or: You can’t have it  both ways. Jeb Bush is either a great candidate or the greatest candidate. Which is it?

16. Complex Question. Drawing a conclusion from a simple answer given to a question that asks two things. E.g., the detective asked you where you hid the stolen money, and you said “nowhere,” so who did you give it to?

17. Suppressed Evidence. Drawing a conclusion from a set of premises which leaves out pertinent information. E.g., Jones and Smith have consumed the same number of drinks tonight, and Jones is still sober, so Smith must be too. (If Smith is 120 lbs and has not had dinner yet, and Jones is 200 lbs and has a full stomach, this conclusion will not follow.)

This fallacy is hard to detect; one needs to have reason to suspect that pertinent information is missing.

“Begging the Question” is the most important name to retain from this set, because it is a phrase used in everyday life quite a bit. Used –and misused. Just recently I heard Brian Williams on NBC Nightly News say “which begs the question why he didn’t reveal this earlier.” All that Mr. Williams meant was “which raises the question.” They are very different things: to beg the question is to “ask” that a controversial point be granted –which means slipping something controversial in.   In contrast, to raise the question is to actually ask the question, whereas begging the question is really more like covering it over and ignoring it. So, what do you make of the argument, “Brian Williams said Scott McClellan’s new book begs the question of why he didn’t say these things earlier, so McClellan’s book must beg the question.” (appeal to unqualified authority: Brian Williams does not really know what “beg the question” means!)

IV. Fallacies of Ambiguity

18. Equivocation. Drawing a conclusion as a result of the ambiguity of the meaning of a word. E.g., Fred said he’s going to give me a ring after work today! We’re going to get married!

19. Amphiboly. Drawing a conclusion as a result of the ambiguity of a grammatical construction. E.g., I’ve never been so insulted! Billy says he likes sushi better than me!

20. Composition. Concluding that the whole has the properties of the parts (or: shifting from universal distributive predication to collective predication) in a situation in which it is unwarranted. E.g., Every page in Don Quixote is very thin, so Don Quixote is a very thin book.

21. Division. Concluding that the parts have the properties of the whole (or: shifting from collective predication to universal distributive predication) in a situation in which it is unwarranted. E.g., Americans are all rich, since America is such a rich country.

“Ambiguity” means “multiplicity of meaning.” In the first two, the issue is whether the meaning that matters (and that changes as you go from premises to conclusion) is a function of a word alone, or a function of sentence structure. In the latter two, which are mirrors of one another, the change of meaning happens because of the subject of predication. That is, it means one thing to say “rich” about the whole made up of all Americans, and another to say “rich” of the individuals who make up that whole — individual Americans. The change can be named as shifting from COLLECTIVE to DISTRIBUTIVE predication in the case of Division, or from DISTRIBUTIVE to COLLECTIVE predication in Composition. These are truly Informal fallacies, i.e., it is not the case that every time you see this move, you are seeing something fallacious.

“The machine is solid gold, so all its parts are made of gold.”   Clearly this is a perfectly good argument. You have to have some relevant empirical knowledge to be able to make the accusation of a fallacy of composition or division.     Advice: everyday, generate or find your own simple examples of these fallacies; this will get you “on top” of the distinctions.

  • Fallacy Identification Exercises

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