A logical fallacy is a pattern of reasoning that is rendered invalid by a flaw, either in its logical structure or in its premises. Fallacies, in their various forms, play a significant role in how people think, and in how they communicate with each other.
The following article serves as a brief, introductory guide to logical fallacies, which will help you understand the different types of fallacies, and allow you to account for them better.
The types of logical fallacies
There are two main types of logical fallacies:
- Formal fallacies- this type of fallacy occurs when there is a flaw in the logical structure of an argument.
- Informal fallacies- this type of fallacy occurs when there is an issue with one or more of the premises of an argument.
Therefore, the difference between formal and informal fallacies is that in the case of formal fallacies there is a flaw in the structure of the argument, while in the case of informal fallacies there is a flaw in the premise of the argument.
For instance, the following is an example of a formal fallacy:
Premise 1: If it’s raining, then the sky will be cloudy.
Premise 2: The sky is cloudy.
Conclusion: Therefore, it’s raining.
Both premises are valid, but the conclusion is not, since there is a flaw in the logic of the argument. Specifically, premise 1 tells us that if it’s raining, then the sky will be cloudy, but that doesn’t mean that if the sky is cloudy (which we know it is, based on premise 2), then it’s necessarily raining. That is, it’s possible for the sky to be cloudy, without it raining.
On the other hand, the following is an example of an informal fallacy:
Premise 1: The weatherman said that it’s going to rain next week.
Premise 2: The weatherman is always right.
Conclusion: Therefore, it’s going to rain next week.
Here, the logical structure of the argument is valid. Specifically, since premise 1 tells us that the weatherman said that it’s going to rain next week, and premise 2 tells us that the weatherman is always right, then based on what we know, we can reasonably conclude that it’s going to rain next week.
However, there is a problem with this reasoning, since premise 2 is flawed, because our assumption that the weatherman is always right is in fact incorrect. As such, even though the logical structure of the argument is fine, the use of a flawed premise means that its final conclusion is invalid.
In the next sections, you will learn a bit more about each type of fallacy, as well as about how they are used, and how to counter them.
As we saw above, formal fallacies involve an invalid argument, where the conclusion does not logically follow from the preceding premises.
An example for this is the masked-man fallacy, where an invalid substitution of two identical entities leads to an invalid conclusion. For example:
Premise 1: The citizens of New York know that Superman saved their city.
Premise 2: Clark Kent is Superman.
Conclusion: The citizens of New York know that Clark Kent saved their city.
The conclusion here is invalid, because even though Superman is in fact Clark Kent, the citizens of New York don’t necessarily know his true identity, and therefore don’t necessarily know that Clark Kent saved their city. As such, even though both the premises are true, there is a flaw in the logical structure of the argument, which renders its conclusion invalid.
As we saw above, an informal fallacy occurs when one or more of the premises in an argument fails to support its proposed conclusion, either because the premises are false, or because they are irrelevant.
An example for this is the strawman fallacy, which occurs when a person distorts their opponent’s argument, in order to make it easier to attack:
Alice: I think we should increase the military budget.
Bob: I disagree, since if we spend the entire federal budget on the military, there won’t be anything left for education or healthcare.
Here, Bob’s argument is valid from a formal, logical perspective: if we spend 100% of the federal budget on the military, there really won’t be anything left to spend on other things, such as education and healthcare.
However, Bob’s reasoning is fallacious, due to his unverified assumption that when Alice suggests increasing the military budget, she actually means that the entire federal budget should be allocated to the military. Essentially, Bob is making a logically-valid argument, but one that is countering an irrelevant point that no one is trying to make.
Just because an argument is fallacious doesn’t mean that it’s wrong
Just because an argument contains a logical fallacy, and is therefore not logically valid, does not mean that its overall conclusion is necessarily false.
Assuming that this is the case is a fallacy in itself, known as the argument from fallacy (or the ‘fallacy fallacy’). This is because an argument can rely on logically-fallacious reasoning, and still be correct.
For instance, let’s go back to the original example that we saw for a formal logical fallacy (which is known as affirming the consequent):
Premise 1: If it’s raining, then the sky will be cloudy.
Premise 2: The sky is cloudy.
Conclusion: Therefore, it is raining.
The conclusion here is invalid, since we can’t be sure that it’s true based on the premises that we have. However, that doesn’t necessarily mean that the conclusion is false. In fact, it’s entirely possible that it is raining, we just can’t conclude this based on the premises that we were given.
The same holds for informal fallacies. For example, consider the following argument:
Alison: it’s amazing how accurate my horoscope is.
John: no it isn’t. Horoscopes are nonsense.
Here, John is using an appeal to the stone (an informal fallacy), by dismissing Alison’s argument as absurd without providing any proof as to why. However, that doesn’t mean that he’s wrong; even though John uses fallacious reasoning, his argument against horoscopes is still right, as shown by research on the topic.
Overall, this shows that an argument can contain faulty reasoning, whether in the form of a formal or an informal fallacy, and yet still lead to a conclusion that is factually correct.
Countering logical fallacies
Being able to counter logical fallacies is important, both when other people use them in discussions, as well as when you rely on them in your own thought process. Each fallacy is countered in a slightly different way, and specific guides for each are available in my posts on logical fallacies. However, the basis for countering them all is to point out the issue with the reasoning that leads to the logical fallacy in the first place.
The appeal to nature, for example, is a fallacy which assumes that something is good because it is “natural”, or bad because it is “unnatural”. The best way to counter it is by giving specific counterexamples which show that things which are “natural” can be bad and that things which are “unnatural” can be good, or by demonstrating the issues with trying to define what “natural” means in the first place.
When you counter fallacies that other people use, it’s important to remember that not every use of a logical fallacy is intentional, and to act accordingly. Specifically, attacking your opponent too forcefully for using a fallacious argument might lead to a backfire effect, where they are not willing to change their mind on the topic, even after you show them the problem with their reasoning. Therefore, where possible, try to assume that the person you are talking to is not using fallacious arguments on purpose, and help them internalize the error in their reasoning, by pointing it out in a non-confrontational manner.
Summary and conclusions
- Logical fallacies occur as a result of invalid or faulty reasoning, and play a significant role in people’s thought process and communication.
- There are two main types of fallacies: formal fallacies, which occur when there is a flaw in the logical structure of an argument, and informal fallacies, which occur when one or more of the premises in an argument fails to support the proposed conclusion, either because it’s irrelevant, or because one or more of its premises are false.
- Example for a formal fallacy: based on the premises that “if it’s raining, then the sky will be cloudy” and “the sky is cloudy”, then we conclude that “it’s raining”. Specifically, based on these premises alone, we cannot logically conclude that it’s raining just because it’s cloudy.
- Example for an informal fallacy: based on the premises that “the weatherman said that it’s going to rain next week” and “the weatherman is always right”, then we conclude that “it’s going to rain next week”. Here, the logical structure of the argument is valid, but the conclusion is not, because one of the premises is incorrect (since the weatherman isn’t always right).
- It’s important to remember that an argument can rely on fallacious reasoning and still have a correct conclusion. Assuming that a conclusion is incorrect just because the argument used to reach it is invalid represents a logical fallacy in itself, known as the ‘argument from fallacy’.