Yeah, the person making the assertion can be wrong.

for there to be a fundamental shift in reality.

Huh? Did you read what I wrote:

It doesn't just mean X is going to happen if the laws of the universe remain the same [...] It means that X happens in every possible version of our universe from this point onward

Every. Possible. Universe. This accounts for "fundamental shift[s] in reality".

It is not so easy to separate assertions and evidence, Logos01. An assertion is in itself evidence - strong evidence perhaps, depending on who it comes from and in what context. Evidence is entanglement with reality, and the physical phenomenon of someone having said or written something can be entagled with what you want to know about in just the same way that any other type of evidence is entangled with reality.

For example if you were to ring your friend and ask him for the football results, you would generally update your degree of belief in the fact that your team won if he told you so (unless you had a particular reason to mistrust him). You would not wait until you had been provided with television footage and newspaper coverage of the result before updating, despite the fact that he had given you a mere assertion.

That is a trivial example, because you apparently are in need of one to gain understanding.

If someone quotes Yudkowsky as saying something, depending on how impressed you are with him as a thinker you may update on his mere opinions (indeed, rationality may demand that you do so) without or before considering his arguments in detail. Authorities may be "unreliable", but it is the fallacy of grey to suggest that they therefore provide no evidence whatsoever. For that matter, your own sensory organs are unreliable - does this lead you not to update your degree of belief according to anything that you see or hear?

Since Yudkowsky is widely respected in intellectual terms here, someone might quote him without feeling the need to provide a lengthy exposition of the argument behind his words. This might be because you can easily follow the link if you want to see the argument, or because they don't feel that the debate in question is worth much of their time (just enough to point you in the right direction, perhaps).

On the other hand it is true that argument screens off authority, and perhaps that is what you are imperfectly groping towards. If you really want to persuade anyone of whatever it is you are trying to say, I suggest that you attempt to (articulately) refute Yudkowsky's argument, thereby screening off his authority. Don't expect anyone to put your unsupported opinions together with Yudkowsky's on the same blank slate, because you have to earn that respect. And for that matter, Yudkowsky actually has defended his statements with in-depth arguments, which should not really need to be recapitulated every time someone here references them. His writings are here, waiting for you to read them!

... it doesn't follow that because authorities are unreliable, their assertions without supporting evidence should not adjust your weighting in belief on any specific claim?

Being less than a perfect oracle does not make an information source worthless.

It's like saying that because a coin has come up heads every time you've flipped it before it's now likely to come up heads this time.

I'm puzzled and wonder if I'm missing your point because this update makes perfect sense to me. Let's say that I start for a prior for whether the coin is fair, P(fair), a prior for whether it is biased towards heads, P(headbiased), and a prior for whether it is biased towards tails P(tailbiased). My updated probability for P(headbiased) increases if I get lots of heads on the coin and few or no tails. It'll probably help if we understand each other on this simpler example before moving on to appeals to authority.

You must of course allow for the possibility of the other person being mistaken, otherwise you would simply substitute their probability estimate for your own. But to fail to update on the fact of someone's belief prior to obtaining further information on the reliability of their mechanisms for determining the truth means defaulting to an assumption of zero reliability.

We wrote:

I simply thought your response indicated that you were not aware that "Rational behaviour is whatever makes you win" was a reference to an established ideology,

As to whether it is "established ideology" or not: "frankly, my dear, I don't give a damn."

I thought it meant:

I simply thought your response indicated that you were not aware that "Rational behaviour is whatever makes you win" was a reference to a previously-described idea,

As to whether it is "a previously-described idea" or not: "frankly, my dear, I don't give a damn."

I'm pretty sure you thought it meant:

I simply thought your response indicated that you were not aware that "Rational behaviour is whatever makes you win" was a reference to a sacred LW doctrine,

As to whether it is "sacred LW doctrine" or not: "frankly, my dear, I don't give a damn."