A false premise is an incorrect proposition or assumption that forms the basis of an argument and renders it logically unsound.
For example, in the argument “all birds can fly, and penguins can’t fly, so penguins aren’t birds”, the premise that “all birds can fly” is false, since some birds can’t fly, and this renders the argument logically unsound.
Accordingly, an argument that contains false premises can be referred to as an argument from false premises.
Because false premises are common, and because they stand at the core of many logical fallacies, it’s important to understand them. As such, in the following article you will learn more about false premises, see how you can respond to their use by others, and understand what you can do to avoid using them yourself.
Examples of false premises
An example of a false premise is “all swans are white”, which can appear, for instance, in a logically unsound argument such as “all swans are white, so if an animal is black then it isn’t a swan”.
Another example of a false premise appears in the following syllogism (a form of reasoning where a conclusion is drawn from two premises):
Premise 1: If the street is wet, then it just rained.
Premise 2: The street is wet.
Conclusion: It just rained.
Here, premise 1 (“If the street is wet, then it just rained”) is false, since if the street is wet, that doesn’t necessarily mean that it just rained. For example, it’s possible that it rained hours ago and the street didn’t dry, or that a fire hydrant broke and sprayed water everywhere.
Because this argument relies on a false premise, it can be considered logically unsound. However, this doesn’t mean that the conclusion of the argument is necessarily false, since even fallacious arguments can have true conclusions, which means that it’s possible that it did indeed just rain.
In addition, further examples of false premises appear as part of various logical fallacies.
For example, the appeal to nature is a logical fallacy that can involve claiming that something is good because it’s “natural”. Here, the premise that “natural” things are necessarily good for you is false, since there are many “natural” things that are bad for you, such as cyanide, which is a deadly toxin that’s produced naturally by some plants.
Another example of false premises that stand at the core of a logical fallacy appears in the case of the false dilemma, which is a logical fallacy that occurs when a limited number of options are incorrectly presented as being mutually exclusive to one another or as being the only options that exist, in a situation where that isn’t the case. False dilemmas contain at least one of the following false premises:
- Mutual exclusivity. In this context, mutual exclusivity means that only one of the available options can be selected (or can be true) at any given time. When the premise of mutual exclusivity is false, this means that it involves presenting the available options in a way that suggests that we can only choose one of them (or that only one of them can be true), while in reality it’s possible to pick two or more of them (or for two or more of them to be true). For example, this can involve saying that either A or B are true, even though in reality both can be true at the same time.
- Collective exhaustivity. In this context, collective exhaustivity means that the options that are presented are the only ones that are available. When the premise of collective exhaustivity is false, this means that it involves presenting a limited number of options as the only available ones, while in reality there are additional relevant options. For example, this can involve saying that we must choose between options A or B, even though option C also exists.
False premises and logical fallacies
A logical fallacy is a pattern of reasoning that contains a flaw, either in its logical structure or in its premises.
Many logical fallacies rely on false premises. This includes, for example:
- The appeal to novelty. The appeal to novelty occurs when something is assumed to be either good or better than something else, simply because it’s perceived as being new and novel. For example, a person using the appeal to novelty might claim that a certain new exercise plan that a celebrity just came up with is better than traditional alternatives, simply because it’s newer. This is based on the false premise that something being new necessarily means that it’s better than older things.
- The argument from incredulity. The argument from incredulity occurs when someone concludes that since they can’t believe something is true, then it must be false, and vice versa. For example, someone using the argument from incredulity might claim that since they don’t see how a certain scientific theory could be true, then it must be false. This is based on the false premise that one’s inability to believe that something is true means that it must necessarily be false.
- The fallacy fallacy. The fallacy fallacy occurs when someone assumes that if an argument contains a logical fallacy, then its conclusion must be false. For example, someone using the fallacy fallacy might claim that if an argument in favor of a certain political stance is fallacious, then that stance must necessarily be wrong. This is based on the false premise that if an argument contains a logical fallacy, then its conclusion must be false, even though that’s not necessarily the case.
False premises are a feature of informal logical fallacies in particular, which are logical fallacies that occur when there is a flaw in the premises of an argument, which renders the argument logically unsound. These fallacies are contrasted with formal logical fallacies, which occur when there is a flaw in the logical structure of an argument, which renders the argument logically invalid.
However, informal fallacies can also be fallacious for other reasons than that they contain false premises, such as that they rely on premises that are irrelevant to the discussion, as in the case of the red herring fallacy.
Explicit and implicit premises
Premises can either be explicit, which means that they are mentioned directly as part of an argument, or implicit, which means that they are hinted at and used as part of the argument without being mentioned directly.
For example, in the argument “all birds can fly, and penguins can’t fly, so penguins aren’t birds”, the premise that all birds can fly is explicit, since it is stated directly. Conversely, in the argument “penguins can’t fly, so they’re not birds”, the premise that all birds can fly is implicit, because it’s not mentioned directly, but it is hinted at and used as part of the argument.
Both true and false premises can be either explicit or implicit. However, explicit premises can’t be implicit and vice versa, since the two qualities are mutually exclusive.
The decision of whether a given premise should be explicit or implicit depends on various factors. For example, someone might choose to rely on a certain true premise implicitly during a discussion, because they believe that this premise is obvious to all participants, so there’s no point in mentioning it explicitly. Conversely, someone might choose to rely on an implicit false premise while giving a speech, because making that premise implicit makes it harder for listeners to notice the issues with it.
How to respond to false premises
To respond to the use of false premises, you should generally call them out as being false, explain why they’re false, and if necessary also explain how them being false invalidates the argument that they’re a part of. For example, if someone says “this product is all-natural, so it’s good for you”, you can say that just because something is natural that doesn’t mean that it’s good for you, and then give relevant examples that illustrate this.
When doing this, it’s important to remember that false premises can be implicit, rather than explicit. For example, in the argument “this product is all-natural, so you should buy it”, the false premise that things that are natural are good for you is implicit, since it’s not mentioned directly. When this is the case, you might have to also point out the existence of the premise and the role that it plays in the argument, before you can call it out for being false.
In addition, it can sometimes be beneficial to ask the person who relied on the false premise to support it. For example, this might be beneficial in cases where it helps the other person notice and internalize the errors in their reasoning, or in cases where you’re not sure if a certain premise is false in the first place. When doing this, you can also remind the other person that the burden of proof is on them, since they’re the ones who made the argument in question.
Finally, there are also two caveats that are important to keep in mind when responding to false premises.
First, while the presence of false premises renders an argument logically unsound, it doesn’t necessarily mean that its conclusion is false. For example, consider the following argument:
Premise 1: The weatherman said that it’s going to rain tomorrow.
Premise 2: The weatherman is always right.
Conclusion: It’s going to rain tomorrow.
Premise 2 in this argument can be false if the weatherman isn’t always right. However, even if this is the case, that doesn’t mean that the conclusion of the argument is false, since it’s possible that it’s still going to rain tomorrow; we just don’t know whether it’s necessarily going to rain based on this argument alone.
Second, false premises aren’t always crucial from a practical perspective, and they don’t necessarily invalidate an argument’s main point. This can happen, for example, if the false premise plays a relatively minor role in the argument, or if the argument could be easily revised to account for the issue with the premise. In such cases, it can be better to either ignore the false premise entirely, or to point out the issue with it, while acknowledging that the main point of the argument still holds.
In this regard, it can be helpful to keep the following quote in mind:
“All great historical and philosophical arguments have probably been fallacious in some respect. But it is unlikely that any extended argument has ever actually been fallacious in all respects. Complex theses are great chains of reasoning. The fact that one link in the chain is imperfect does not mean that other links are necessarily faulty, too. If the argument is a single chain, and one link fails, then the chain itself fails with it. But most historians’ arguments are not single chains. They are rather like a kind of chain mail which can fail in some part and still retain its shape and function. If the chain mail fails at a vital point, woe unto the man who is inside it. But not all points are vital points.”
— From “Historians’ Fallacies: Toward a Logic of Historical Thought” (By David Hackett Fischer, 1970)
Overall, to respond to the use of false premises, you can ask the person who made them to justify them, call out the premises as being false and explain why they’re false, and if necessary also explain how them being false invalidates the argument that they’re a part of. When doing this, keep in mind that false premises can be implicit, and that their presence doesn’t necessarily invalidate an argument’s main point or mean that the argument’s conclusion is necessarily false.
How to avoid using false premises
To avoid using false premises, you should make sure that you’re aware of all the premises that your argument is based on, and that you know for certain that these premises are true. If necessary, you can clearly outline arguments that you make, by stating what your premises are, what your conclusion is, and how you derive that conclusion based on your premises. Furthermore, you can engage in self-distancing, by treating your arguments as if they were presented by someone else, which can help you analyze the arguments in a more rational manner.
When doing this, it’s important to consider not only the explicit premises in your arguments, but also the implicit ones, which aren’t mentioned directly. In addition, it’s important to remember that when you make an argument, the burden of proof is on you to properly support your premises, and it’s generally not other people’s responsibility to disprove your unsupported claims.
If you’re uncertain whether a premise is true or false, you can sometimes still include it in your argument in a reasonable way, as long as you modify your argument accordingly. For example, you might do this by saying the following:
“I’m not sure that this premise is true, but assuming that it is, my argument is that…”
Finally, to help yourself avoid false premises, it can be beneficial to learn about common fallacies that are associated with false premises, such as the appeal to nature and the fallacy fallacy. This can help you learn to avoid the specific false premises associated with them, and can also help you identify and understand other types of false premises. Furthermore, this can also help you become better at countering the use of false premises by others, by teaching you to identify and understand such premises.
Overall, to avoid using false premises, you should make sure that you’re aware of all the premises that your argument is based on, and that you know for certain that these premises are true. To achieve this, it can help to clearly outline your argument, to analyze your argument as if it was presented by someone else, to remind yourself of your burden of proof, and to familiarize yourself with common fallacies that rely on false premises.
Summary and conclusions
- A false premise is an incorrect proposition or assumption that forms the basis of an argument and renders it logically unsound.
- For example, in the argument “all birds can fly, and penguins can’t fly, so penguins aren’t birds”, the premise that “all birds can fly” is false, since some birds can’t fly, and this renders the argument logically unsound.
- To respond to the use of false premises, you can ask the person who made them to justify them, call out the premises as being false and explain why they’re false, and if necessary also explain how them being false invalidates the argument that they’re a part of.
- When responding to false premises, keep in mind that false premises can be implicit, and that their presence doesn’t necessarily invalidate an argument’s main point or mean that the argument’s conclusion is necessarily false.
- To avoid using false premises, you should make sure that you’re aware of all the premises that your argument is based on, and that you know for certain that these premises are true; to achieve this, it can help to clearly outline your argument, to analyze your argument as if it was presented by someone else, to remind yourself of your burden of proof, and to familiarize yourself with common fallacies that rely on false premises.