Logical fallacies
What are logical fallacies?
What are logical fallacies?
What are logical fallacies?
A Formal Fallacy
An Informal Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Ad Hominem Fallacy
Your turn...�
See if you can tell which of these is an ad hominem argument, and which is just an insult...
Example 1
Example 2
Strawman Argument�
Strawman argument
Strawman argument
Your turn...�
See if you can detect how both of the following responses could qualify as a strawman argument.
Senator: “Driving a car with low emissions, such as a Prius, could help to reduce our impact on the environment.”
Response A Response B
“The Senator thinks we can solve all our ecological problems by driving a Prius.”
“Quite the contrary, the Senator thinks the environment is such a wreck that no one’s car choice or driving habits would make the slightest difference.”
Appeal to Ignorance (argumentum ad ignorantiam)�
Appeal to ignorance
Appeal to ignorance
Your turn...
Consider the following examples. Can you spot the appeal to ignorance?
Example 1
Example 2
False Dilemma/False Dichotomy�
False Dilemma/False Dichotomy�
False Dilemma/False Dichotomy�
Your turn...
Slippery slope fallacy...
Slippery slope fallacy...
Slippery slope fallacy...
Your turn...
Example 1
Example 2
Circular reasoning (petitio principii)
Circular reasoning (petitio principii)
Your turn...
Example 1
Example 2
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Hasty generalisation...
Your turn...
Which of the following is a hasty generalization?
Example 1
Example 2
Red Herring Fallacy (ignoratio elenchi)
A “red herring fallacy” is a distraction from the argument typically with some sentiment that seems to be relevant but isn’t really on-topic. This tactic is common when someone doesn’t like the current topic and wants to detour into something else instead, something easier or safer to address. A red herring fallacy is typically related to the issue in question but isn’t quite relevant enough to be helpful. Instead of clarifying and focusing, it confuses and distracts.
Red Herring Fallacy (ignoratio elenchi)
A red herring fallacy can be difficult to identify because it’s not always clear how different topics relate.
The phrase “red herring” refers to a kippered herring (salted herring-fish) which was reddish brown in color and quite pungent. According to legend, this aroma was so strong and delectable to dogs that it served as a good training device for testing how well a hunting dog could track a scent without getting distracted. Dogs aren’t generally used for hunting fish so a red herring is a distraction from what he is supposed to be hunting.
Red Herring Fallacy (ignoratio elenchi)
A red herring fallacy can be difficult to identify because it’s not always clear how different topics relate. A “side” topic may be used in a relevant way, or in an irrelevant way. In the big meaty disagreements of our day, there are usually a lot of layers involved, with different subtopics weaving into them. We can guard against the red herring fallacy by clarifying how our part of the conversation is relevant to the core topic.
Your turn...
Example 1
Example 2
Tu Quoque/Appeal to hypocrisy
Tu Quoque/Appeal to hypocrisy
Your turn...
Which of the following is a tu quoque fallacy?
Example 1
Example 2
Causal fallacy
The causal fallacy is any logical breakdown when identifying a cause. You can think of the causal fallacy as a parent category for several different fallacies about unproven causes.
One causal fallacy is the false cause or non causa pro causa ("not the-cause for a cause") fallacy, which is when you conclude about a cause without enough evidence to do so. Consider, for example, “Since your parents named you ‘Harvest,’ they must be farmers.” It’s possible that the parents are farmers, but that name alone is not enough evidence to draw that conclusion. That name doesn’t tell us much of anything about the parents. This claim commits the false cause fallacy.
Causal fallacy
Another causal fallacy is the post hoc fallacy. Post hoc is short for post hoc ergo propter hoc ("after this, therefore because of this"). This fallacy happens when you mistake something for the cause just because it came first. The key words here are “post” and “propter” meaning “after” and “because of.” Just because this came before that doesn’t mean this caused that. Post doesn’t prove propter. A lot of superstitions are susceptible to this fallacy. For example:
“Yesterday, I walked under a ladder with an open umbrella indoors while spilling salt in front of a black cat. And I forgot to knock on wood with my lucky dice. That must be why I’m having such a bad day today. It’s bad luck.”
Causal fallacy
Now, it’s theoretically possible that those things cause bad luck. But since those superstitions have no known or demonstrated causal power, and “luck” isn’t exactly the most scientifically reliable category, it’s more reasonable to assume that those events, by themselves, didn’t cause bad luck. Perhaps that person’s "bad luck" is just their own interpretation because they were expecting to have bad luck. They might be having a genuinely bad day, but we cannot assume some non-natural relation between those events caused today to go bad. That’s a Post Hoc fallacy. Now, if you fell off a ladder onto an angry black cat and got tangled in an umbrella, that will guarantee you one bad day.
Causal fallacy
Another kind of causal fallacy is the correlational fallacy also known as cum hoc ergo propter hoc (Lat., “with this therefore because of this"). This fallacy happens when you mistakenly interpret two things found together as being causally related. Two things may correlate without a causal relation, or they may have some third factor causing both of them to occur. Or perhaps both things just, coincidentally, happened together. Correlation doesn’t prove causation.
Consider for example, “Every time Joe goes swimming he is wearing his Speedos. Something about wearing that Speedo must make him want to go swimming.” That statement is a correlational fallacy. Sure it’s theoretically possible that he spontaneously sports his euro-style swim trunks, with no thought of where that may lead, and surprisingly he’s now motivated to dive and swim in cold, wet nature. That’s possible. But it makes more sense that he put on his trunks because he already planned to go swimming.
Your turn...
Which kind of causal fallacy is at work in these examples?
Example 1
Example 2
Example 3
Fallacy of sunk costs...
Sometimes we invest ourselves so thoroughly in a project that we’re reluctant to ever abandon it, even when it turns out to be fruitless and futile. It’s natural and usually not a fallacy to want to carry on with something we find important, not least because of all the resources we’ve put into it. However, this kind of thinking becomes a fallacy when we start to think that we should continue with a task or project because of all that we’ve put into it, without considering the future costs we’re likely to incur by doing so. There may be a sense of accomplishment when finishing, and the project might have other values, but it’s not enough to justify the cost invested in it.
Fallacy of sunk costs...
We are susceptible to this errant behavior when we crave that sense of completion or a sense of accomplishment
“Sunk cost” is an economic term for any past expenses that can no longer be recovered. For example, after watching the first six episodes of Battlestar Galactica, you decide the show isn’t for you. Those six episodes are your “sunk cost.” But, because you’ve already invested roughly six hours of your life in it, you rationalize that you might as well finish it. All apologies to Edward James Olmos, but this isn’t "good economics" so to speak. It’s more cost than benefit.
Fallacy of sunk costs...
Psychologically, we are susceptible to this errant behavior when we crave that sense of completion or a sense of accomplishment, or we are too comfortable or too familiar with this unwieldy project. Sometimes, we become too emotionally committed to an “investment,” burning money, wasting time, and mismanaging resources to do it.
Your turn...
Example 1
Example 2
Appeal to Authority (argumentum ad verecundiam)
Appeal to Authority (argumentum ad verecundiam)
Appeal to Authority (argumentum ad verecundiam)
Appeal to Authority (argumentum ad verecundiam)
Your turn...
Example 1
Example 2
Example 3
Equivocation (ambiguity)
Equivocation (ambiguity)
Your turn...
How do each of these examples commit an equivocation fallacy?
Example 1
Example 2
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Appeal to Pity/Emotion (argumentum ad misericordiam)�
Your turn...
Which of these is a fallacious appeal to emotion, and which one is not?
Example 1
Example 2
Bandwagon fallacy
The bandwagon fallacy assumes something is true (or right, or good) because other people agree with it. A couple different fallacies can be included under this label, since they are often indistinguishable in practice. The ad populum fallacy (Lat., “to the populous/popularity”) is when something is accepted because it’s popular. The concensus gentium (Lat., “consensus of the people”) is when something is accepted because the relevant authorities or people all agree on it. The status appeal fallacy is when something is considered true, right, or good because it has the reputation of lending status, making you look “popular,” “important,” or “successful.”
Bandwagon fallacy
For our purposes, we’ll treat all of these fallacies together as the bandwagon fallacy. According to legend, politicians would parade through the streets of their district trying to draw a crowd and gain attention so people would vote for them. Whoever supported that candidate was invited to literally jump on board the bandwagon. Hence the nickname “bandwagon fallacy.”
Bandwagon fallacy
This tactic is common among advertisers. “If you want to be like Mike (Jordan), you’d better eat your Wheaties.” “Drink Gatorade because that’s what all the professional athletes do to stay hydrated.” “McDonald’s has served over 99 billion, so you should let them serve you too.” The form of this argument often looks like this: “Many people do or think X, so you ought to do or think X too.”
Bandwagon fallacy
One problem with this kind of reasoning is that the broad acceptance of some claim or action is not always a good indication that the acceptance is justified. People can be mistaken, confused, deceived, or even willfully irrational. And when people act together, sometimes they become even more foolish — i.e., “mob mentality.” People can be quite gullible, and this fact doesn’t suddenly change when applied to large groups.
Your turn...
Which of these is a bandwagon fallacy?
Example 1
“Almost everyone at my school will be at the party Friday night. It must be a popular thing to do.”
Example 2
“Almost everyone at my school will be at the party Friday night. It must be the right thing to do.”