Blogosophy

Can Dr. Evil reason from this premise: "The PDF are trying to persuade me not to press the button"? Elga's thought is that because Evil and Dup are in the same subjective state, neither can be sure of whether:

(1) My interactions with the PGF are the result of their trying to persuade me to not push the button.

or

(2) My interactions with the PGF are the result of their trying to persuade someone else (named Dr. Evil) to not push the button.

Since it's part of the setup of the problem that the PGF don't lie, they really do have to build a duplicate and send him letters, etc. But I think Elga is going to say that one cannot be sure that the PGF is really trying to persuade one to not push the button. All one knows is that they are trying to persuade Dr. Evil, and one is meant to be unsure of whether one is Dr. Evil or not. Consider how all Dr. Evil's evidence (on usual theories of evidence) is neutral as between (1) and (2). That is to say, Dup's deception is a matter of his being deceived as to who he is (at least until he reads the letter). Won't this deception extend to his beliefs about whether the PGF is trying to persuade him to not push the button?

I don't think the priors, or the veracity of the PDF (and particularly the steps they take so that their ambiguous statements can be true) really matter. What if they sent the following letter:

Dear Dr. Evil,

Either you are completely at our mercy, or you are not. You know this to be logically true, so you need not even consider our veracity. If you are at our mercy, and you press the button to fire your "laser" we shall torture you. Since you do not wish to be tortured, you should not press the button.

Cordially,
The PDF

Should Dr. Evil accept this argument? If not, then why should Dr. Evil accept the original argument that having taking extraordinary measures so that it is contingently true that Dr. Evil either is or is not at the PDFs mercy, he should refrain? I guess what I don't see is how phrasing it as an epistemological argument (for all you know, you may be at our mercy) makes it stronger than the bare you either are or are not at our mercy. Perhaps that amounts to the same as your objection in the end...

I guess what I don't see is how phrasing it as an epistemological argument (for all you know, you may be at our mercy) makes it stronger than the bare you either are or are not at our mercy.

Here's the difference. Saying to Dr. Evil (1) "Either you are Dr. Evil or not" is definitely right, and Dr. Evil knows its right (we may imagine) because it's a logical truth. The difference between Dr. Evil getting your letter and getting Elga's is that in your case it should be clear that Dr. Evil knows which disjunct of (1) is true - he knows that he is Dr. Evil. And so you're right that a letter featuring (1) would not compel him to give up his belief that he's Dr. Evil.

But if the letter says "For all you know, you're not Dr. Evil" and Dr. Evil accepts that (based on the existence of the duplicate, etc.), then he does not know which of the disjucnts of (1) is true, and if he thinks that he doesn't know that, he ought to give up his belief that he's Dr. Evil.

Note that in Elga's version of the letter from the PGF, they do not address him as "Dr. Evil" - they open the letter with "Dear Sir," and make a note of never referring to the recipient as "Dr. Evil" - since they mean to without lying give the same letter to Dup.

I guess I wasn't clear. I'm wasn't intending to repeat the duplicate experiment with a different letter; I was considering whether the bare assertion of the logical possibility that pushing the button could result in torture ought to dissuade Dr. Evil. Obviously not. Nor does it change things (as far as I can see) if the letter included a catalog of logically possible but empirically unverifiable ways that it might be true, e.g. duplicate, brain in a jar, eternal damnation after death, deceitful demon, teleporting sharks with lasers on their heads, squads of invisible boyscouts surrounding him ready to tackle him, etc. No matter how many of these you pile up, I suspect Dr. Evil ought to remain unmoved. So what does the PDF scenario actually add to that? Well, the posit that Dr. Evil believes the PDF to be truthful when they say that one of these scenarios is actually true of someone in the world. But is that actually relevant evidence?