Does Descartes’ argument for dualism commit the masked man fallacy?

Suppose that I see a bank being robbed. As a result, I believe that the masked man robbed the bank. Later, a detective tells me that their suspect is my father. I say that the masked man has a property that my father doesn’t: he’s someone I believe to have robbed the bank.

Here’s the formal argument:

1. The masked man has the property of being someone I believe robbed the bank
2. My father lacks the property of being someone I believe robbed the bank
3. Therefore, my father is not identical with the masked man.

This is a bad argument because it could still be the case that my father is the masked man, despite both premises being true. What this illustrates is that arguing along this style is invalid when the property in question involves someone’s psychological attitude.

Now is Descartes’ argument similar?

1. My body possesses the property of being something the existence of which I doubt
2. I don’t posses the property of being something the existence of which I doubt
3. Therefore, I am not identical with my body

2 thoughts on “Does Descartes’ argument for dualism commit the masked man fallacy?

  1. I am afraid that is not quite consistent with Descartes arguments. Rather he establishes that the mind is not merely something that he chooses to doubt, but actually has a nature that he can be certain of since he knows it must exist while he is thinking. If you must reduce it to a simple deductive outline it would be more like:

    1) The mind has a metaphysical nature that allows it to know for certain it exists independent of whether or not the body exists.
    2) The body does not have this metaphysical nature. If the body exists as people usually presume it does, then it interacts with the mind intimately. But it does not share the nature of being directly evident by the natural light that the mind does when one thinks.

    Conclusion: the mind and body are distinct in that they have at least one clear difference in their natures.

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