A logical fallacy is an erroneous pattern of reasoning that contains a flaw, either in its structure or in its underlying premises. Fallacies, in their various forms, play a significant role in how people think and in how they communicate with each other, so it’s important to understand them.
The following article serves as an introductory guide to logical fallacies, which will help you understand what logical fallacies are, what types of them exist, and what you can do in order to counter them.
What is a logical fallacy
A logical fallacy can be defined as a pattern of reasoning which is considered fallacious due to a flaw in its logical structure or in its premises.
An example of a logical fallacy is the argument from incredulity, which occurs when someone concludes that since they can’t believe that a certain concept is true, then it must be false, and vice versa. For instance, this fallacy is demonstrated in the following saying:
“I just can’t believe that humans could have evolved naturally from unicellular organisms. There is no way that evolution is right.”
In this case, the speaker’s pattern of reasoning is considered fallacious, because they have a flaw in their premises, and specifically in their assumption that if they can’t believe that humans evolved naturally, then that means that the theory of evolution is wrong.
The types of logical fallacies
There are two main types of logical fallacies:
- Formal fallacies- a formal logical fallacy occurs when there is a flaw in the logical structure of an argument, which renders the argument invalid.
- Informal fallacies- an informal logical fallacy occurs when there is an issue with one or more of the premises of an argument, which renders the argument unsound.
Therefore, there are two differences between formal and informal fallacies. First, formal fallacies contain a flaw in their logical structure, while informal fallacies contain a flaw in their premises. Second, formal fallacies are considered to be invalid patterns of reasoning, while informal fallacies are considered to be unsound patterns of reasoning, despite the fact that they can still be valid.
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: It’s raining.
Though both the premises in this example are true, the argument is considered to be invalid, since there is a flaw in its logical structure.
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, which is why we can’t reach the conclusion that is specified in the argument, and which is why this argument is invalid, despite the fact that its premises are true.
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: 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 logically conclude that it’s going to rain next week.
However, there is still a problem with this line of reasoning, since our assumption that the weatherman is always right (premise 2) is incorrect. As such, even though the logical structure of the argument is valid, the use of a flawed premise means that the overall argument is considered to be unsound.
Overall, we can say that a sound argument is one that has a valid logical structure and true premises. A formal logical fallacy means that the argument is invalid, due to a flaw in its logical structure, which also means that it’s unsound. An informal logical fallacy means that the argument is unsound, due to a flaw in its premises, though it can still have a valid logical structure.
Example of a formal logical fallacy
As we saw above, a formal fallacy occurs when there is an issue with the logical structure of an argument, which renders the argument invalid.
An example of a formal logical fallacy 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 Metropolis 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.
This argument is invalid, because even though Superman is in fact Clark Kent, the citizens of Metropolis don’t necessarily know Superman’s true identity, and therefore don’t necessarily know that Clark Kent saved their city. As such, even though both the premises of the argument are true, there is a flaw in the argument’s logical structure, which renders its conclusion invalid.
Example of an informal logical fallacy
As we saw above, an informal fallacy occurs when there is an issue with the premises of an argument, which renders the argument unsound, either because the premises are untrue or because they are irrelevant.
An example of an informal logical fallacy is the strawman fallacy, which occurs when a person distorts their opponent’s argument, in order to make it easier to attack. For example:
Alice: I think we should increase the education budget.
Bob: If we spend the entire federal budget on education, there won’t be anything left for the military or for healthcare.
Here, Bob’s argument is valid from a formal, logical perspective: if we spend 100% of the federal budget on education, there won’t be anything left to spend on other things, such as the military and healthcare.
However, Bob’s reasoning is fallacious, due to his false (or at the very least unverified) premise that when Alice suggests that we should increase the education budget, she actually means that the entire federal budget should be allocated to education. Essentially, Bob is making a logically-valid argument, but one that is countering an irrelevant point that no one is trying to make.
How to respond to 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 different ones are available in my posts on logical fallacies. However, there is a lot of similarity in terms of how different logical fallacies can be countered, and in most cases the basic technique for countering a logical fallacy involves pointing out the flaw in reasoning and explaining why it’s an issue.
The appeal to nature, for example, is an informal fallacy which assumes that something is good because it’s perceived as “natural”, or bad because it’s perceived as “unnatural”. The best way to counter the appeal to nature 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.
Because you want to point out the flaw in reasoning that is caused by the use of a logical fallacy, it’s beneficial to remember the distinction that we saw earlier between formal and informal fallacies.
Specifically, when trying to explain why your opponent’s reasoning is fallacious, try to examine whether the flaw is in the logical structure of their argument (which signifies the use of a formal fallacy), or in the premises of their argument (which signifies the use of an informal fallacy). This can help you identify which area of your opponent’s reasoning is flawed, and will help you explain why this flaw invalidates their argument.
Finally, it’s also important to keep in mind that sometimes, when responding to the use of fallacious reasoning, dismantling the logic behind your opponent’s reasoning and highlighting its flaws might not work. This is because, in practice, human interactions and debates are highly complex, and involve more than just exchanging logically sound arguments with one another.
Accordingly, you should accept the fact that, in some cases, you might have to rely on various different strategies in order to respond to the use of a logical fallacy. This can involve anything from refusing to engage with fallacious arguments entirely, to modifying your own arguments in order to respond to the fallacious reasoning without explicitly addressing the fact that it is fallacious.
Account for unintentional use of fallacies
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 a topic, even after you show them their reasoning is flawed.
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.
In addition, remember that you too might be using logical fallacies unintentionally in your thinking and in your communication with others. To identify cases where you are doing this, try to examine your reasoning, and see if you can identify any flaws, either in the way that your arguments are structured, or in the premises that you rely on in order to make those arguments. Then, try to adjust your reasoning, in order to avoid making these errors.
Remember that just because an argument is fallacious, that doesn’t mean that its conclusion is wrong
It’s important to remember that just because a certain line of reasoning is fallacious, that does not mean that its overall conclusion is necessarily incorrect. 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: It’s 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 incorrect. 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:
Alice: It’s amazing how accurate my horoscope is.
Bob: No it isn’t. Horoscopes are nonsense.
Here, John is using an appeal to the stone (which is 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, since even though John uses fallacious reasoning, his conclusion regarding 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. To assume otherwise is fallacious, which is why you shouldn’t discount people’s argument immediately, just because they contain a fallacy.
The difference between logical fallacies and cognitive biases
While logical fallacies and cognitive biases appear to be similar to each other, they are two different things:
- Logical fallacies are flawed patterns of reasoning (a philosophical concept).
- Cognitive biases are systematic errors in cognitive processing (a psychological concept).
Accordingly, cognitive biases are said to occur at a more basic level of thinking, and they can lead to the use of various logical fallacies.
For example, the appeal to novelty is a logical fallacy that causes people to assume that something is either good because it’s perceived as “new”, or bad because it’s perceived as “old”. It’s possible that some people are predisposed to this fallacy due to a cognitive bias that causes them to instinctively prefer things which they view as being more modern. However, this isn’t necessarily the case, and people can use arguments which rely on the appeal to novelty even if they don’t truly believe in them.
Overall, the main difference between logical fallacies and cognitive biases is that logical fallacies are a philosophical concept, while cognitive biases are a psychological one. In some cases, the occurrence of a certain cognitive bias can promote the use of a logical fallacy, but logical fallacies can also be used even if they are unprompted by any cognitive bias.
Summary and conclusions
- Logical fallacies are flawed patterns of reasoning, which play an important 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 there is an issue with the premises of an argument, either because they’re untrue or because they’re irrelevant.
- An example of a formal fallacy is the following: 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.
- An example of an informal fallacy is the following: 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 argument is unsound, because one of the premises is flawed (since the weatherman isn’t always right).
- To successfully counter the use of a logical fallacy, you will generally have to identify the flaw in reasoning, point it out, and explain why it’s problematic. The optimal way to do this varies between different fallacies, and remembering the distinction between formal and informal fallacies can help you in this process.