The probability that people will believe a long conjunction is less probable than they will believe one part of the conjunction (because in order to believe both parts, they have to believe each part. In other words, for the same reason the conjunction fallacy is a fallacy.)
The conjunction fallacy is the assignment of a higher probability to some statement of the form A&B than to the statement A. It is well established that for certain kinds of A and B, this happens.
The fallacy in your proof that this cannot happen is that you have misstated what the conjunction fallacy is.
My point in mentioning it is that people committing the fallacy believe a logical impossibility. You can’t get much more improbable than a logical impossibility. But the conjunction fallacy experiments demonstrate that is common to believe such things.
Therefore, the improbability of a statement does not imply the improbability of someone believing it. This refutes your contention that “the probability that people believe something shouldn’t be that much more than the probability that the thing is true.” The possible difference between the two is demonstrably larger than the range of improbabilities that people can intuitively grasp.
What about the conjunction fallacy?
The probability that people will believe a long conjunction is less probable than they will believe one part of the conjunction (because in order to believe both parts, they have to believe each part. In other words, for the same reason the conjunction fallacy is a fallacy.)
The conjunction fallacy is the assignment of a higher probability to some statement of the form A&B than to the statement A. It is well established that for certain kinds of A and B, this happens.
The fallacy in your proof that this cannot happen is that you have misstated what the conjunction fallacy is.
My point in mentioning it is that people committing the fallacy believe a logical impossibility. You can’t get much more improbable than a logical impossibility. But the conjunction fallacy experiments demonstrate that is common to believe such things.
Therefore, the improbability of a statement does not imply the improbability of someone believing it. This refutes your contention that “the probability that people believe something shouldn’t be that much more than the probability that the thing is true.” The possible difference between the two is demonstrably larger than the range of improbabilities that people can intuitively grasp.
I wish I had thought of this.