The Masked-Man Fallacy: Twisting Arguments Through Invalid Substitutions

The Masked-Man Fallacy

 

The masked-man fallacy is a logical fallacy where the substitution of two identical entities leads to a flaw in the logic of an argument. A classic example for this fallacy is the following:

Premise 1: I know who my father is.

Premise 2: I don’t know who the masked-man is.

Fallacious conclusion: the masked-man is not my father.

Intuitively, we know that this conclusion is fallacious, since I cannot be certain that my father is not the masked-man, based on these premises alone. The following article will show you the logical flaw in this type of reasoning, and explain the role that this fallacy plays in everyday arguments.

 

Understanding the masked-man fallacy

The masked-man fallacy is a formal logical fallacy, meaning that its reasoning is rendered invalid by a flaw in its logic. Specifically, this flaw lies in the fact that substituting two identical entities can change the truth value of a statement, when the statement says something about our knowledge of the world.

Simply put, this means that even if character A and character B are the same person, the fact that we know different things about each character means that we cannot freely substitute one for the other. Consider the following example:

Premise 1: Bruce Wayne is Batman.

Premise 2: Batman saved Gotham.

Conclusion: Bruce Wayne saved Gotham.

Since Bruce Wayne is in fact Batman, it is true that if Batman saved Gotham, then we can say that Bruce Wayne saved Gotham. Here, since we are talking about facts, we can substitute these two characters freely.

However, the same doesn’t hold if we’re talking about people’s knowledge of these facts. Consider the following example:

Premise 1: The citizens of Gotham know that Batman saved their city.

Premise 2: Bruce Wayne is Batman.

Fallacious conclusion: The citizens of Gotham know that Bruce Wayne saved their city.

The conclusion in this example is obviously invalid, since the citizens of Gotham don’t necessarily know that Bruce Wayne saved their city. Even though Bruce Wayne and Batman are the same person from a logical perspective, the fact that people know something about one of them, doesn’t mean that they know the same thing about the other.

Note: This fallacy is based on the concept of identity of indiscernibles (also referred to as Leibniz’s law). Essentially, this concept means that if two entities have the exact same properties, then they are identical. However, what people know about an entity is not considered a property of that entity. Therefore, the fact that Bruce Wayne and Batman are identical (from a logical perspective), doesn’t mean that people’s knowledge of them is also identical.

 

The masked-man fallacy in arguments

This fallacy appears in arguments whenever an invalid substitution occurs, as we saw in the examples above. That is, it occurs when someone takes for granted that just because we know something about X, then it means that we also know something about Y, if X and Y are different representations of the same thing.

In arguments and debates, this fallacy is often used in conjunction with a strawman argument to attack people, by stating that their support for a person or an idea based on one aspect, means that they also support a different aspect of that person or idea.

Consider the following theoretical example:

Alice: I support the plan to reduce federal healthcare coverage.

Bob: So you’re saying you support a plan for killing thousands of poor citizens.

Bob is twisting Alice’s stance in order to make it easier to attack, by using an invalid substitution. Specifically, while it is possible that he is indeed correct, and that the plan that Alice is supporting (reducing healthcare coverage) is also a plan with the same outcome that Bob describes (killing thousands), that does not mean that that is what Alice is supporting in her mind.

This distinction is crucial: what people know about something is distinct from the properties of that object. Even if this plan has the same outcome that Bob predicts, it’s incorrect to assume that Alice supports this aspect of the plan. If Bob wants to avoid using this fallacy, he can make a similar but modified argument against Alice’s stance:

Alice: I support the plan to reduce federal healthcare coverage.

Bob: The problem is that this plan will lead to the deaths of thousands of poor citizens.

Here, Bob’s argument against the plan itself is similar, but he doesn’t use fallacious reasoning to suggest that Alice directly supports the plan to kill thousands of people. Instead, he argues directly against the plan that Alice supports, without assuming that she supports the aspects of the plan that he finds problematic.

 

Countering the masked-man fallacy

The initial strategy for countering this sort of argument is pointing out the flaw in your opponent’s logic. You do this by showing why your opponent’s reasoning is fallacious, and that just because you support X, does not mean that you also support Y.

However, while doing this is valid from a logical perspective, the problem is that it doesn’t help you argue against whatever point your opponent is trying to make against your stance. Furthermore, if you focus too much on the gap in their reasoning, there is the risk that you will appear to implicitly agree with their overall point, which is whatever negative thing they are saying about your stance.

Therefore, you need to make sure that after briefly highlighting the gap in your opponent’s logic, you move on to defending your main stance. For example:

Alice: I support the plan to reduce federal healthcare coverage.

Bob: So you’re saying you support a plan for killing thousands of poor citizens.

Alice: I am definitely not saying that I support such a plan. When did you hear me say that?

Bob: Well, you might not think that, but this will be the outcome of the plan to reduce federal healthcare coverage.

Alice: I disagree with what you’re saying. Recent statistics show…

Here, Alice first points out the flaw in Bob’s reasoning, while simultaneously putting him on the defensive. Then, after Bob is forced to adjust his original, fallacious argument, Alice moves on to argue against his main attack on her stance.

 

Using the masked-man fallacy

You might be using the masked-man fallacy yourself when attacking your opponent’s arguments. This happens whenever you substitute one aspect of their stance for a different aspect of that stance that is often more difficult for them to defend, as we saw above.

The difference between doing this and using a logically-sound argument is that here, you are essentially attacking your opponent’s supposed beliefs, instead of attacking the stance for which they express support.

The problem with using this type of arguments, beyond the inherent issue with relying on logically fallacious reasoning, is that by making your attack more personal, you will usually put the person you are arguing with in a defensive mode, where they automatically reject your argument. This can cause them to support their original stance more strongly, even if you manage to make a good point overall.

Overall, you can avoid using this fallacy yourself by being critical of your reasoning process. Specifically, you should ensure that you don’t make any unverified assumptions about people’s knowledge of the world, which could lead you to rely on invalid substitutions when building your arguments.

 

Summary and conclusions

  • The masked-man fallacy is a logical fallacy where the substitution of two identical entities leads to a logical flaw in the reasoning process, as a result of the different knowledge that we have about each entity.
  • For example, if Bruce Wayne is Batman, and the citizens of Gotham know that Batman saved their city, it would be incorrect to assume that the citizens of Gotham know that Bruce Wayne saved their city.
  • In everyday arguments, this technique is used when people assume that because someone supports one aspect of an idea (e.g. reducing healthcare coverage), then it means that they also support other aspects of that idea (e.g. killing poor people). Even though both aspects may be true, it is incorrect to assume that if someone supports one of them, then they also know about and support the other aspects of that idea.
  • You can counter this fallacy by briefly pointing out the flaw in your opponent’s reasoning and putting them on the defensive, before moving on to attack the main point in their argument.
  • Remember that you might also be using this fallacy yourself, in cases where you make unverified assumptions about your opponent’s knowledge, and attack their supposed beliefs instead of addressing the actual stance that they support. Doing this generally lead to more personal arguments, which could make your opponent less willing to listen to what you have to say.