PHIL102 Study Guide


Unit 5: Fallacies

5a. Explain fallacies of inconsistency, irrelevance, insufficiency, and inappropriate presumption

  • What is a fallacy?
  • What is an inconsistency fallacy?
  • What is an irrelevance fallacy?
  • What is an insufficiency fallacy?
  • What is an inappropriate presumption fallacy?

    We have learned how good arguments are those that not only satisfy the criteria for validity and soundness in deductive arguments, or cogency and strength in inductive arguments, but are also convincing, as a result of those features. More technically, we've seen that an argument is formally convincing when it is valid or strong (for deductive and inductive evaluations, respectively). Even better is when the argument is valid or strong, and the premises are actually true (sound or cogent, for deductive and inductive arguments, respectively). Interestingly enough, we often come across "good" arguments without really committing ourselves to believing what those arguments prove. At the same time, we may be moved to a firm belief by poor arguments. Why? Shouldn't we be utterly convinced by sound and cogent arguments, but dismiss those that aren't any good?

    Argumentation is not simply an attempt to prove that something is the case; it's also an attempt to persuade. Unfortunately, a poor argument can convince someone not only to believe something, but also to act upon this belief. In fact, some bad arguments can be very convincing because they fool us into believing the premises justify the conclusion, or by attacking us, or by simply distracting us. Other bad arguments are deceptive because they rely on ambiguity in our language and grammar. This unit focuses on patterns of bad reasoning known as fallacies.

    A fallacious argument is deceptive, erroneous, or misleading. In short, a fallacy is a flawed reasoning. With few exceptions, the patterns of fallacious reasoning do not fall into exclusive categories. If you look at a handful of logic and critical thinking texts, you might see different groupings of fallacies, as well as different fallacy identifications. For example, one text might list one pattern of fallacious reasoning under the category Fallacies of Relevance, while another might list it under Fallacies of Weak Induction. While the groupings are meant to make it easier to identify fallacies as instances of a category, they aren't strict. What is important for you to remember is how to identify each fallacy pattern, and why the fallacy is occurring. More importantly, you should focus on being able to analyze the reasoning:

    1) Identify the premise(s) and conclusion;
    2) Reorganize and reformulate the argument to highlight the weakness of the inference;
    3) Explain how and why the reasoning fails; and
    4) Explain why one should avoid the type of reasoning under consideration.

    Once you've worked through the fallacies, you will see why they are grouped together as they are, but how they're grouped is not essential to your working understanding of them. The last section of this unit will identify another mode of fallacious argumentation known as formal fallacies. This type of fallacy occurs when an argument looks very similar in structure to one of the deductive argument forms, but is slightly off, thereby misleading you to believe the conclusion follows when, in fact, it does not.

    A legitimate question is, "Why is reasoning this way instead of that way better?" There are several ways to answer this question, but the least straightforward one is that there are rules of reasoning that are apparently fundamental to reason itself. Uncovering those rules is part of the task of logic.

    Another, related answer is that justifications for claims we make should be relevant to the claim itself, and relevant in a way that actually achieves or demonstrates the conclusion. Think about it this way: The conclusion of a valid argument is demonstrated by the premises; it is extracted, as it were. All that's required to infer the conclusion is an understanding of the meanings of the terms, for example, or the structure of the reasoning.

    Here is an example:

    A is identical to B.
    B is identical to C.
    A is identical to C.

    Notice that experience is not required to see how the conclusion drops out, as it were, from the premises. Instead, one need only understand the meaning of the phrase, "is identical to", in order to make the inference.

    This is also the case when the inference fails:

    Aloysius likes Bertrand.
    Bertrand likes Josh.
    Aloysius likes Josh.

    Liking someone is not transitive in the way that, for example, the spatial relation expressed by "to the left of", is. So, whereas the "likes" argument fails, this one does not:

    Aloysius is to the left of Bertrand.
    Bertrand is to the left of Josh.
    Aloysius is to the left of Josh.

    Even when experience guides our reasoning, as is the case with inductive arguments, we are pretty adept at determining when a particular instance of reasoning succeeds or fails. Consider these two examples:

    It has rained every day this week.
    The forecast calls for rain again tomorrow.
    It will rain tomorrow.

    I just met a really cute person.
    That person looks like my ex, sounds like my ex, makes similar gestures as my ex made, and even has the same sense of humor.
    I remember, though, that I broke up with my ex because of a series of lies.
    This really cute person is a liar, too.


    Perhaps what is most important for your studies is not only learning the ways in which one can reason well and reason poorly, but learning and practicing new ways to reason, so you become more in command of your decisions and beliefs. In this way you can begin to see how different logical systems work, and evaluate them for yourself. The ability to think for yourself – not simply to be outspoken and opinionated, but to have a grasp of the variety of ways people can draw conclusions and support them – is crucial to making judgments about the world.

    Consider, for a moment, the term "objective". When you say that someone is being objective, or that you know something to be objectively true, you are making an important claim. If reasoning is not objective, it is nearly impossible for anyone to talk to anyone else about it. For in that case, reason would be relative to each individual, and there would be no communication. When we understand the domain of discourse, and we understand how to present and evaluate reasoning, we're in a much better position to succeed in nearly every endeavor we undertake. When we say that we can evaluate reason objectively, we mean that we can talk about how reason works without bringing into the discussion our individual beliefs and attitudes. As a disposition, "objectivity" here means impartiality, or refusal to be swayed by any one person's thoughts, feelings, and attitudes. So, when we're talking about reasoning well, and making claims that we can distinguish between good and bad reasoning, we are saying that we can be objective about how reason works. As mentioned above, this means we think we can create or uncover rules of reason that apply to all rational beings – in other words, we say that reasoning has universal rules.

    There is a sharp contrast made between reasoning well and reasoning poorly. This contrast is based on the idea that inferences are made logically; that is, either deductively or inductively. Deductive inferences are said to be necessary, while inductive inferences are said to be probable. There is more ambiguity in evaluating inductive arguments than there is in evaluating deductive arguments. This is because there are degrees of probability, which is the defining feature of inductive arguments, while there are no degrees of necessity, which is the defining feature of valid arguments. In other words, deductive arguments have a much stricter requirement for their being good than do inductive arguments. Even deductive arguments can be subject to degrees of being good because it can be valid but not sound. Moreover, a deductive argument can seem perfectly acceptable until you detect an error due to, say, a grammar problem. This is why it's so important for you to develop your ability to judge the merits of the reasoning you come across in your daily life, and the reasoning you do yourself every day.

    Reasoning fails in a variety of ways – so many, in fact, that grouping them according to common features is a helpful way to organize our thinking. Inconsistency fallacies involve the advancement and acceptance of an inconsistency or self-defeating argument. Inappropriate presumption fallacies occur when the argument includes an unreasonable assumption. Relevance fallacies occur when the premises and conclusion are not relevant to each other, or relevant premises are ignored. Finally, fallacies of insufficiency occur when the premises provide insufficient support for the conclusion.

    To review, see What is a Fallacy?  


    5b. Identify common fallacies, including the straw man, gambler's fallacy, begging the question, red herring, ad hominem, appeal to ignorance, appeal to people, complex question, loaded question, and non-sequitur

    • What is the straw man fallacy?
    • What is the gambler's fallacy?
    • What is the begging the question fallacy?
    • What is the red herring fallacy?
    • What is the ad hominem fallacy?
    • What is the appeal to ignorance fallacy?
    • What is the appeal to people fallacy?
    • What is the complex question fallacy?
    • What is the loaded question fallacy?
    • What is a non-sequitur?

      The straw man fallacy is a distraction fallacy, and so there is no relevance between premises and conclusion. In a straw man fallacy, two arguments are presented. One of the arguments is presented as being so weak – it is presented as being flimsy like a straw man –  that it is easy to dismiss it. At that point, another argument is brought in as a better option. The problem is that the presentation of that first argument is a distortion of the original. It is this distortion that makes the alternative seem more reasonable by comparison. The problem with such reasoning is that it doesn't present the opposing argument accurately. Indeed, one likely would not recognize the original when presented with the distorted version. Moreover, by not presenting the opposing argument as strongly as possible, the alternative presented becomes simply the only one left – it's not one that wins out on its own merits.

      Below are some examples of straw man arguments.

      Example 1:

      Sandra is opposed to wearing helmets when riding bicycles. Apparently, the number of critical and fatal injuries that are the result of not wearing proper headgear is not important to her. She must also be against wearing seatbelts in cars or having wings on planes. Even worse, people drive so irresponsibly, riding a bike without a helmet is practically asking for a car to hit you. Not wearing headgear is like playing roulette with your life.  Instead, everyone should wear headgear because it protects from major injuries in the case of bicycle accidents.

      Example 2:

      Senator Joe Politick is seeking to require every student below the age of sixteen to attend public high school.  Basically, he wants to take away students' and parents' rights to educate as they see fit.  t's a form of tyranny to make people do things. On top of all this, the public school system is so bad that going there is like not getting an education at all. Students would be wasting seven hours a day just because Joe Politick wants to control their lives. There must not be any compulsory public education if we are to preserve our freedoms as Americans.

      Notice that the positions are stated so radically and with inflammatory language that they essentially work as support for the alternative position. The alternative position barely needs any support in order for it to seem appealing. In the first example, an expressed opposition to wearing helmets is not equivalent to, for example, being opposed to wearing seatbelts. In the second example, the proposed requirement to attend public high school is not the same as wanting to take anyone's rights away from them.

      Begging the question occurs when the premises implicitly or explicitly are found in the conclusion so that the reasoning becomes circular. In this fallacy, what you want to prove is already assumed to be true, so you're not actually proving anything. "The Bible says God exists. I know this is true because God says so". Whereas in a nonfallacious argument it is the premises that support the conclusion, in a question begging argument, the conclusion supports the premises, which support the conclusion.

      Below are some examples of begging the question.

      Example 1:

      Euthanasia is morally wrong, since it's wrong to murder people.

      Example 2:

      It is good to use fuel-efficient and hybrid cars.  So, of course people should drive fuel-efficient and hybrid cars.

      Example 3:

      This book is the best novel ever written because no other novel is as good.

      The problem with the first example is it begs the question, how do we know that euthanasia is murder? The second example begs the question, why is it good to use fuel-efficient and hybrid cars? The last example's conclusion is simply a restatement of the premises using slightly different wording.

      The gambler's fallacy involves erroneous reasoning about probabilities. More specifically, when we believe that random events can influence each other, such as that a series of coin tosses are related, we commit the gambler's fallacy. Suppose, for example, that you have bought a lottery ticket every day for the past week. Each ticket has lost, but you conclude that, since you've lost a bunch of times in a row, you are going to win soon.

      Red herring is a rather strange name, but it's actually quite appropriate to the fallacy that bears it. Hunters presumably used the first, red herring, to train dogs how to hunt. The fish are purportedly dragged across the ground in an effort to distract the dog from a scent. Those best trained will not be deterred from it, however, while the others are led astray. The fallacy does something very  similar. One person tries to distract another or others from a conclusion. Suppose, for example, a teenager comes home after curfew. As the teen walks in the door, the waiting parent says, "Just what were you doing coming home after curfew?" Instead of addressing the question, the teen says, "Look! Is that a cockroach running across the floor?"

      That is an obvious (and, one hopes, unsuccessful) attempt to distract from the issue at hand. Below are some examples of red herring.

      Example 1:

      Mr. Langford claims that wearing helmets to ride bicycles is an important safety precaution. I remember taking long bike rides with my family when I was younger. We would ride for hours at a time along country roads. Those were such great memories.

      Example 2:

      Many people are opposed to genetically modified food. The study of genetics is crucial to understanding how the world of living things works. It is especially important since many living things share some of the same genes.

      An ad hominem, (from the Latin, meaning, "to the man") also known as Personal Attack, involves two arguers. The first person presents an argument or a claim, and the second person attacks the first person instead of addressing the argument. These personal attacks take three forms: ad hominem abusive, ad hominem circumstantial, and poisoning the well.

      An ad hominem abusive is most typically an attack against something the individual can't control (such as height, sex, race), but also takes the form of any abuse of the person him or herself (such as calling someone fat or ugly). A circumstantial attack is focused not on the person him or herself, but on associations and affiliations, such as someone's religion, area of residence, political party, and so forth. Poisoning the Well occurs when, even before someone makes his or her case (that is, presents an argument), that person is attacked by someone else. 

      Below are some examples of ad hominem abusive.

      Example 1:

      Reynaldo always argues against studying. He thinks that too much studying keeps one from experiencing life.  He's such a moron, so of course he would think that. He's lazy and stupid, and only claims that you can study too much because he's not smart enough to succeed in academics.

      Example 2:

      Jason thinks it's wrong to wear make-up. He says that make-up is just a way to keep women from showing their true selves. Jason is such a jerk. I mean, he's a guy, so what the heck does he know about make-up?

      Below are some examples of ad hominem circumstantial. 

      Example 1:

      Matthew's always talking about how you should eat meat because meat's good for you. Obviously, he doesn't really care about whether or not it's good for you. His family owns a cattle farm, so of course he's going to try to persuade you to eat meat!

      Example 2:

      Kyle claims it's not healthy for you to eat meat. He also claims that it's cruel to animals. Of course he thinks that! After all, his family owns a health food store that doesn't sell animal products, so he wouldn't want you to eat meat.

      Example 3:

      Brianna and Morgan were talking about cars, and Brianna says that the BMW is the best car made. She's only saying that because her family just bought a BMW.

      Below are some examples of poisoning the well.

      Example 1:

      Zach is such a jerk. Don't let him try to butter you up. He's going to tell and tell you how pretty you are so you'll go out with him, but he's not really sincere.

      Example 2 (an address to an audience): 

      You will hear many lies, many exaggerations, and many false promises. Don't believe them! Mr. Dishonest will say anything to persuade you. Anything except the truth.

      Example 3 (book review):

      No sooner than three paragraphs into this book, you'll rue the day you bought it. You might as well have taken your money and thrown it off a bridge.

      A version of the ad hominem type of fallacy is tu quoque (from the Latin meaning, "you too", or "you're one, too") attacks the person instead of that for which the person argues. It is a way of defending oneself against criticism or suggestion, as if to claim that the point the person is making isn't relevant because the person is something of a hypocrite. True though that may be – the person may very well be a hypocrite – that fact does not make the claim any less true or false. A separate argument about the person's character should be mounted in connection with their hypocrisy. Tu quoque can also occur when one person is representing another or others, and the person responding accuses the one (or group) represented of hypocrisy.

      Below are some examples of tu quoque.

      Example 1:

      Person 1: "You should stop smoking. It's bad for your health and it ruins your voice. On top of all that, it's a stinky habit; all your clothes smell like stale smoke".

      Person 2: "Well, who are you to talk? You were a smoker for years".

      Example 2:

      Person 1: "Please be careful with that car. You've only just got your driver's license, and so you don't have much experience on the road".

      Person 2: "Why should I listen to you? Didn't you drag race downtown when you were my age? Isn't drag racing illegal?"

      Example 3:

      Person 1: "The company President wants all the employees to spend more time volunteering their time to charities".

      Person 2: "She has got to be kidding! She hasn't devoted a day to charity since she's been here, so why should we?"

      The fallacy of ad ignorantiam (from the Latin meaning, "to ignorance") involves drawing a conclusion based on ignorance. Someone is supposed to be forced by ignorance of something into accepting a conclusion that is equally unknown.

      Below are some examples of ad ignorantiam arguments.

      Example 1:

      Aliens don't exist. We've never seen any, so we can't claim that they do.

      Example 2:

      They haven't found any of the bank robber's loot. Therefore, there must not be any.

      Example 3:

      You can't prove that I stole the apple from your store, so you must be wrong about my being guilty of the theft.

      A lack of experience or proof of something existing does not deny that something does in fact exist. In cases of ad ignorantiam arguments, logic would not allow the conclusions. Instead, you would be wise instead to suspend your judgment until better evidence becomes available.

      Ad populum is a mass appeal fallacy. (It comes from the Latin meaning, "to the people"). The problem with Mass Appeal, or Appeal to the Masses, is that the appeals are not relevant to the conclusion insofar as they are appeals to emotion. Advertising is always some version of an appeal to the masses. Appealing to mass numbers of people is not necessarily a bad thing. However, since the appeal is made on emotional grounds and not rational ones, it is logically fallacious. If you read any text on rhetoric, (Aristotle's Poetics is a classic example) you will notice that emotional appeals are not only a very effective way to get people to do or think something, but they are also a perfectly legitimate rhetorical device. We must not mistake logical fallacy, in all instances, as something inherently bad. Nevertheless, good reasoning is not fulfilled by fallacy.

      Below are some examples of ad populum arguments. 

      Example 1 (an advertisement): 

      "Buy Splendid jeans. They're the trendiest, hippest jeans around!"

      Example 2 (a politician):

      "Americans, join me in a great act of patriotism. Join me in bringing America back to its glorious days. A vote for me is a vote for America!

      Example 3 (an advertisement): 

      "Too Cool Cologne isn't for everyone. If you're cool, hip, and with-it, then Too Cool Cologne is for you." 

      The first advertisement represents an appeal to being part of the group. Everyone wants to be accepted, and this ad preys upon that desire. Whether or not Splendid jeans are well-made, comfortable, or durable is not addressed. Instead, only the desire of the consumer to be part of the group is addressed.

      In the second example, a politician associates voting for him with being patriotic. In this example, the details of the politician's plan for the country is not the focus. Most people feel the emotion of patriotism, of loyalty to one's country, rather intensely. Yet, there is no reason to think that anyone is being patriotic by voting for a particular politician. Love of one's country does not necessitate particular actions.

      The third example also appeals to desire. In this case, the desire is to be part of an elite group. It is an appeal to vanity or snobbery. Surely, anyone who thinks they are "cool, hip, and with-it" could succumb to the lure of an advertisement like this.

      A complex question fallacy involves asking (at least) two questions in a single grammatical sentence, which thereby makes it difficult to separate out. So, answering one part of the question thereby commits you to answering the other, as well. For example, you might be asked if you want to take courses in Existentialism and Phenomenology. If you say, "Yes", you are committed to both, when you may really only be interested in Existentialism.

      A loaded question fallacy is one in which another question is hidden. The answer to that hidden question is already presupposed, and so the question forces a specific answer, regardless of whether or not it is authentic.  In numerous instances in which a "yes or no" question is impossible to answer with a "yes" or a "no", there is a complex question fallacy at work. The danger of the complex question is that it is an attempt to trap someone into saying something that's probably not true.

      Below are some examples of the complex question. 

      Example 1:

      Have you stopped lying yet?

      Example 2:

      How did you steal the bagels?

      Each example is really two questions. If you answer "Yes" to the question, "Have you stopped lying yet", then you are admitting you lied. If you answer "No", then you are admitting that you're still lying. (Of  course, that could be a lie!) The question is really two questions: "Were you a liar? If so, are you still lying?" The second example asks for details about a theft that is already presumed to have been committed.

      A non-sequitur is one way to refer to a formal fallacy. Two of the most common errors in reasoning are flawed versions of the modus ponens and modus tollens arguments – the fallacies, affirming the consequent and denying the antecedent mimic the forms of their valid counterparts. It is because of their similarities to these valid deductive argument forms that they gain their persuasiveness. The good thing about recognizing the form of each fallacy is that it applies to any argument structured in the form of affirming the consequent and denying the antecedent. You do not have to analyze the argument's content; you simply need to know how the fallacies look.

      Denying the antecedent: Anytime you see an argument that looks like a combination of the modus ponens and modus tollens forms, but concludes that the consequent is not true because of a negation of the antecedent, you have a formally fallacious argument. Using the counterexample method discussed in Unit 2 makes the error of this form of reasoning clear. 

      Below, a few examples will reveal how this argument form is fallacious.

      Example 1:

      If it's raining, then it's wet.
      It's not raining.
      It's not wet.


      Example 2: 

      If you grill the chicken, it will brown.
      You don't grill the chicken.
      It won't brown.


      Example 3: 

      If you take the bus, you can make the movie on time.
      You didn't take the bus.
      You didn't make the movie on time.

      The problem with the first example is that there are other ways for things to become wet other than rain. Similarly, the second example is one way to brown chicken, but so is frying it or baking it. So it is not correct to conclude that it will not be brown if you don't grill it. In the last example, taking the bus is not the only way to get to the movie on time. Perhaps a ride was offered, or you rode your bicycle.

      Affirming the consequent looks like a reverse modus ponens, or a modus tollens without the negations. In this fallacy, the consequent of the first premise is asserted, and the conclusion is that the antecedent is therefore true. 

      Below are some examples of affirming the consequent. 

      Example 1:

      If you water the lawn every day, the grass will be healthy.
      The grass is healthy.
      You water the lawn every day.


      Example 2:

      If you have five nickels, then you have twenty-five cents.
      You have twenty-five cents.
      You have five nickels.


      Example 3:

      If the lights are on, someone is home.
      Someone is home.
      The lights are on.

      In each example, other conditions could have brought about the consequent. So, the fact that the consequent happened means only that at least one condition obtained, not that that particular one did. In the first example, the grass could be healthy because it rained a lot. Similarly, while it is true that five nickels make twenty-five cents, so does a quarter, twenty-five pennies, two dimes and a nickel, and so forth. Finally, someone could be home without the lights being on; they could be sleeping, or the power could be out.

      To review, see:


      5c. Describe the nature of a cognitive bias and identify examples of cognitive bias

      • What is a cognitive bias?
      • What are some examples of cognitive bias?

        A cognitive bias is a habit of mind, particularly one of which we are unaware. Cognitive biases can influence our thinking away from objectivity, and lead to erroneous reasoning. Examples of cognitive biases are confirmation bias, framing bias, the overconfidence effect. We exhibit confirmation bias when we look for information that confirms an existing view. In so doing, we exclude from consideration evidence that would undermine that view. A framing bias involves influencing an outcome by way of how information is framed. Finally, when we overestimate our skills or abilities, we fall prey to the overconfidence effect.

        To review, see:


        Unit 5 Vocabulary

        This vocabulary list includes the terms listed above that you will need to know to successfully complete the final exam.

        • fallacious argument
        • fallacy
        • inconsistency fallacies
        • inappropriate presumption fallacies
        • relevance fallacies
        • fallacies of insufficiency
        • straw man fallacy
        • begging the question fallacy
        • gambler's fallacy
        • red herring fallacy
        • ad hominem fallacy
        • ad ignorantiam fallacy
        • ad populum fallacy
        • complex question fallacy
        • loaded question fallacy
        • non-sequitur
        • denying the antecedent
        • affirming the consequent
        • cognitive bias