In the first case, you have independent evidence that the conclusion is false, so you’re basically saying “If I considered your arguments in isolation, I would be convinced of your conclusion, but here are several pieces of external evidence which contradict your conclusion. I trust this external evidence more than I trust my ability to evaluate arguments.”
In the second case, you’re saying “I have already concluded that your conclusion is false because I have concluded that mine is true. I think it’s more likely that there is a flaw in your conclusion that I can’t detect than that there is a flaw in the reasoning that led to my conclusion.”
The person in the first case is far more likely to respond with “I don’t know” in response to the question of “So what do you think the real answer is, then?” In our culture (both outside, and, to a lesser but still significant degree inside LW), there is a stigma against arguing against a hypothesis without providing an alternative hypothesis. An exception is the argument of the form “If Y is true, how do you explain X?” which is quite common. Unfortunately, this form of argument is used extensively by people who are, as you say, entirely wedded to a particular conclusion, so using it makes you seem like one of those people and therefore less credible, especially in the eyes of LWers.
Rereading your comment, I see that there are two ways to interpret it. The first is “Rationalists do not use this form of argument because it makes them look like people who are wedded to a particular conclusion.” The second is “Rationalists do not use this form of argument because it is flawed—they see that anyone who is wedded to a particular conclusion can use it to avoid updating on evidence.” I agree with the first interpretation, but not the second—that form of argument can be valid, but reduces the credibility of the person using it in the eyes of other rationalists.
In the first case, you have independent evidence that the conclusion is false
“Independent evidence” is a tricky concept. Since we are talking Bayesianism here, at the moment you’re rejecting the argument it’s not evidence any more, it’s part of your prior. Maybe there was evidence in the past that you’ve updated on, but when you refuse to accept the argument, you’re refusing to accept it solely on the basis of your prior.
In the second case, you’re saying “I have already concluded that your conclusion is false because I have concluded that mine is true.”
Which is pretty much equivalent to saying “I have seen evidence that your conclusion is false, so I already updated that it is false and my position is true and that’s why I reject your argument”.
Not quite, your priors might be good. We’re talking here about ignoring evidence and that’s a separate issue from whether your priors are adequate or not.
Because the case where you are entirely wedded to a particular conclusion and want to just ignore the contrary evidence would look awfully similar...
Awfully similar, but not identical.
In the first case, you have independent evidence that the conclusion is false, so you’re basically saying “If I considered your arguments in isolation, I would be convinced of your conclusion, but here are several pieces of external evidence which contradict your conclusion. I trust this external evidence more than I trust my ability to evaluate arguments.”
In the second case, you’re saying “I have already concluded that your conclusion is false because I have concluded that mine is true. I think it’s more likely that there is a flaw in your conclusion that I can’t detect than that there is a flaw in the reasoning that led to my conclusion.”
The person in the first case is far more likely to respond with “I don’t know” in response to the question of “So what do you think the real answer is, then?” In our culture (both outside, and, to a lesser but still significant degree inside LW), there is a stigma against arguing against a hypothesis without providing an alternative hypothesis. An exception is the argument of the form “If Y is true, how do you explain X?” which is quite common. Unfortunately, this form of argument is used extensively by people who are, as you say, entirely wedded to a particular conclusion, so using it makes you seem like one of those people and therefore less credible, especially in the eyes of LWers.
Rereading your comment, I see that there are two ways to interpret it. The first is “Rationalists do not use this form of argument because it makes them look like people who are wedded to a particular conclusion.” The second is “Rationalists do not use this form of argument because it is flawed—they see that anyone who is wedded to a particular conclusion can use it to avoid updating on evidence.” I agree with the first interpretation, but not the second—that form of argument can be valid, but reduces the credibility of the person using it in the eyes of other rationalists.
“Independent evidence” is a tricky concept. Since we are talking Bayesianism here, at the moment you’re rejecting the argument it’s not evidence any more, it’s part of your prior. Maybe there was evidence in the past that you’ve updated on, but when you refuse to accept the argument, you’re refusing to accept it solely on the basis of your prior.
Which is pretty much equivalent to saying “I have seen evidence that your conclusion is false, so I already updated that it is false and my position is true and that’s why I reject your argument”.
I think both apply.
In fact that case is just a special case of the former with you having bad priors.
Not quite, your priors might be good. We’re talking here about ignoring evidence and that’s a separate issue from whether your priors are adequate or not.