A logical fallacy is an error in reasoning that undermines the logic of an argument. Every claim needs strong supporting evidence, and logical fallacies are usually identified because they lack the sufficient evidence to make that claim, and tend to base their conclusions on an incorrect reasoning process. If the reasoning behind an argument contains a logical fallacy, it is usually invalid or irrelevant. To make your arguments more defensible, avoid using logical fallacies to explain your points, and look out for fallacies in others’ arguments.
Below are some common logical fallacies, their explanations and some examples.
An argument ad hominem, Latin for “to the man”, counters a claim by attacking the person who made that statement, instead of arguing against the claim itself.
You don’t know anything because you’re just a child.
In this example, the statement says that a child made that claim, therefore their claim must be invalid. However, the statement does not actually address the content of the claim, and simply dismisses it based on the premise that the speaker is a child.
This reasoning states that a claim is valid because it was made by a person with authority or credibility.
My professor uses this software, so it is probably the best.
The statement makes an appeal to the authority of the professor, assuming that because the professor has more academic credibility and authority over the students, their choice of software must be justified. However, the statement does not look into the aspects of the software that make it worth using or not.
You may have heard the phrase “jumped on the bandwagon”, which is an example of this fallacy. You may also have seen the bandwagon when people line up at long queues or follow others just because it seems everyone else is doing so. Also called ad populum, the bandwagon is an argument that a claim is valid because many other people think it is.
All the pedestrians just ignored the traffic light. Let’s go ahead and cross too.
If the example situation above was presented instead as “Everyone is jaywalking but it is against the law”, there would probably be a more clear cut answer as to whether the action is right or not. Many people doing something that is wrong does not turn it into the right thing to do.
Also called circular reasoning, begging the question is a form of reasoning that assumes the contested claim is already true.
Ghosts are real. I know that because I saw one with my own eyes.
The example claims that “ghosts are real”, based on the premise “I saw one with my own eyes”. However, for someone to see a ghost and think it is one, they must already believe in the existence of ghosts – or they would probably be finding some other reason to explain what they saw, such as a prank or a trick of the light. Thus, the premise here does not serve any purpose to prove that the claim is true, because it already assumes so.
A false dilemma is an argument that claims there are only two available options, when there is at least one other possible option.
If you are not right-handed, then you must be left-handed.
Of course, there is also the option of being ambidextrous, so this statement is a false dilemma.
However, it is important to note that not all either/or situations are false dilemmas. Sometimes, there may really only be two options, or there may be other options but the speaker is not offering them as a possibility. For example:
Waiter: Would you like coffee or tea?
Customer: Do you have lemonade?
Waiter: Sorry, we only serve coffee or tea for breakfast. You’ll have to purchase a lunch item if you want lemonade as an option.
A hasty generalization draws a conclusion based on an unreasonably small sample size (especially if a larger or more accurate statistic is available).
I eat six fast food meals a day and don’t get fat, so I don’t think fast food is really that bad.
If more people were to eat six fast food meals a day and then study their body mass over an extended period of time, they may find different results as everyone has a different metabolic rate.
It is worth noting, however, that it is acceptable to use a small sample size if obtaining a larger sample size is impossible or not available. For example, if you entered a room full of dust and sneezed immediately, it would not be fallacious to assume that the dust caused you to sneeze.
An argument that omits important information to state that something is the cause of a result, even though that something may only be one of many contributing factors or there may be multiple causes.
Children have been learning bad words on the Internet. Therefore, if we remove their Internet access, then they won’t learn any more bad words.
While it may be reasonable to consider the Internet one of the sources where children can learn bad words, they could also learn it from other places, such as from their peers or on TV shows. As such, it is fallacious to assume that barring their Internet access will entirely solve the problem.
Post hoc, ergo propter hoc, usually shortened to “post hoc”, is an argument stating that because event B occurred after event A, event A must have caused event B. A common example can be seen when some children get diagnosed with autism shortly after receiving a vaccination, causing their parents to think that the vaccine was responsible for the autism.
The drought only started after that woman moved to this village. She must be a witch.
Sadly, there were many cases of post hoc reasoning in the period of witch trials, where people often assumed that when the untimely arrival of a new person preceded a time of bad weather, ailing crops or diseases, that person must be the one responsible for it.
A red herring is an argument that attempts to divert attention from a previous argument by presenting something that is not actually related to the claim. It is done with the deliberate intention to derail the argument.
Wife: I read your mail. Did you seriously just get fired?
Husband: Darling, why would you read my mail? It’s not ethical to do so.
Wife: It was open on your table when I went in your study. So answer me, did you get fired?
Husband: Really? You went in my study and looked at my stuff? We need to talk about respecting each other’s privacy.
While the wife may or may not have been wrong in reading her spouse’s mail, the husband attempts to avoid answering her question by diverting her attention to other matters.
A slippery slope argument takes a relatively minor first event and links it to a chain of events, each more significant but more improbable than the previous, that finally culminates in a final significant outcome – that is usually also quite unlikely to happen. Slippery slopes tend to present more than two events, but really only two are needed.
If you don’t study hard, you will fail your exams. Then you will become a high school dropout, and you will get into a gang. They’ll kick you out and you will end up living on the street, and eventually you’ll be stealing for your next meal, and we all know that road takes you to jail. Therefore, make sure you study hard.
The probability of failing one’s examinations if they do not study is probably quite high, but as the statement goes on, each subsequent event gets more unlikely. In the end, the probability of ending up in jail is likely next to nothing if one just does not study hard.
Jan 02, 2020