> If and only if the arguer's credibility has no logical connection to their argument, then attacking the arguer is fallacious.

The arguer's credibility does not affect the truth value of any statements, so it's always more useful to argue over why someone is wrong. You cannot guarantee that any segment of the population agrees with your credibility assessments. And these assessments should be established via appeals to factual evidence to begin with, anyhow, if we're to believe they should carry any weight at all. Otherwise, we're arguing over feelings instead of facts.

For people with wild, unsupported claims, it's better to simply take the tact that we have not yet seen evidence that establishes those claims and that what's on offer presently does not meet the necessary burden. In that argument, it really doesn't matter who is making the claim, only that the claim itself is not supported.

The arguer's credibility has no bearing on the truth value of purely logical arguments that can be fully evaluated within the four corners of the argument. Very few scientific assertions fit that rubric. In the ordinary case where a conclusion is at some pointed predicated on an unknown fact, then the credibility of the speaker absolutely matters.

Saying that a person's credibility decides the truth value of the statement requires a causal relationship. To say otherwise is to posit a mechanism via which one's opinions somehow shape reality itself. So it seems to me that our notions of 'fact' might not be aligned?

I understand evaluating someone's credibility as a proxy when I have no means of investigating something. I do not understand it when we are talking about scientific assertions, which must be falsifiable in order to be scientific in the first place.

If you aren't the one attempting falsifying it, then you still have to trust somebody based on their credentials.

If you aren't the one attempting to falsify it, then you have no reason to argue over it to begin with, in which case you won't be making any ad hominem arguments to start with.

If that were the case, most people in this thread shouldn't be posting (arguing) but personally running their own medical trials. Any other source would in some way require trust in that source's credentials.

That's of course a bit black/white to say, most arguments don't hold if you push them to their extremes like that. I said it because I believe (your) arguments like "saying that a person's credibility decides the truth value of the statement requires a causal relationship" are similarly black/white.

So yes, in a way the disagreement hinges on a very strict interpretation of the word "fact" versus a less strict interpretation.

It's also to save time in evaluating claims like these. If you've spent any amount of time arguing about pseudoscientific topics (or considered pseudoscience by some), you must have found that yes you can in theory evaluate all[0] (dubious or not) claims in logical, scientific, falsifiable manner. But at some point, especially in pseudoscientific-ish topics, there will be such a great number of claims[1] that you'll find yourself spending most of the time refuting spurious claims rather than actually getting any further.

At that point, you'll never get to the strict definition of the word "fact" (at least, about the particular claim that is the topic of interest), because the claims just keep piling on faster than you can evaluate them. Allowing for a bit less strict definition, allows you to prune the evaluations greatly, and at least allows you to get somewhere.

Now, that struggle doesn't seem to take place in this thread on HN, but according to user "dumbneurologist" it has taken place before elsewhere. And you're still taking that person's word on a matter of (merely claimed) reputation as well.

So yes, there is something to say for taking someone's reputation into account. But it's a pragmatic reason. If you had all the time in the world to dig into everything as deep as you want, you wouldn't strictly need to. But since we do not live in this perfect world, we can and probably should shortcut to the more interesting points of debate by including reputation.

That's the best I can argue this, I think :) It's still a choice, however. You can still choose to only accept strict facts (including "I don't know" when more specific strict facts are unavailable).

[0] ok, not all of them

[1] part of the definition of pseudoscience, where you keep adjusting or special-casing gaps in your hypothesis when it doesn't fit the data, almost necessitates this

> If that were the case, most people in this thread shouldn't be posting (arguing) but personally running their own medical trials. Any other source would in some way require trust in that source's credentials.

We're not discussing the study but logic, so that's really not germane.

> It's also to save time in evaluating claims like these.

You can save far more time by ignoring them.

> The arguer's credibility does not affect the truth value of any statements

It is evidence which you should weigh in deciding how much credence to give their statements.

> so it's always more useful to argue over why someone is wrong.

It's a tradeoff, so there's no obvious bright line with which everyone will agree. But certainly there are some people for which some arguments or claims can be reasonably dismissed out of hand, relative to the preferences of the person making this decision.

If it's evidence, then it must have an effect on the truth or falsity of the statements. So if X says "the sky is blue" then X's credibility must be causally related to whether or not the sky is blue. As there's no such mechanism, this is pointless.

You essentially point out that it's an easy shortcut. And it is, but there's no good reason to take it. One's feelings of credibility do not change the truth value of any statements and so arguments over it are not useful. You will end up arguing over whose feelings are superior and not over observable facts.

When presented with a statement, what matters is the probability that the statement is true. The credibility of a source is strong evidence in this regard and can be used to sway the probability mightily. You're right, of course, that arguing over the credibility is pointless, but an appeal to authority is not fallacious if you and I both agree on the authority.

(Though an appeal to authority is a perfect setup for a motte-and-bailey, so it's important to be wary. Also, it is not, nor ever can be, proof, since that should hold irrespective of authority.)

Yes, I can understand using a mental shortcut by evaluating something simpler that's well-correlated with the truth value. However, this generally runs afoul of Goodhart's law at some point and we invest entirely too much work into something that's meant to be a shortcut.

Moreover, when it's an argument, you want others to agree with you. If you have to take shortcuts and infer the truth of something by proxy because you are either too lazy or not capable of evaluating the matter directly, you probably have no business arguing over it in the first place when you could instead apply your expertise to show how wrong it is.

Worse, your own correlations work against you, as you can now correlate that someone who cannot or will not do that work in making an argument, dragging irrelevant (if sometimes correlated) things into the argument becomes a signal for someone using non-factual means to persuade, which necessarily correlates quite strongly with making false claims.

In short, yes, it can be simpler and it can lead you to being right, if for the wrong reasons. But nobody else has good cause to trust it, it's vulnerable to manipulation, and it's simply better in all cases to be less lazy and fully explain why something is wrong using facts instead of opinions of someone's credibility.

Reality is stochastic. Scientific debates are grounded in probability, not formal logic. If someone has published 38 papers which were complete junk, that gives us a very strong prior about their 39th paper.

Poor researchers are very common. Conspiracies to smear people are very rare. If an academic has a bad reputation, the odds are good that their reputation is deserved.

None of this is conclusive - mavericks do occasionally produce brilliant-but-unconventional research - but it's hugely relevant. There aren't enough hours in the day to give every paper the benefit of the doubt. We have to use Bayesian shortcuts and crude heuristics to filter things for credibility, otherwise we'd be drowning in a sea of junk. The occasional false-positive is a price worth paying.

It's fine to use that to say what is and isn't worth attention. It's not fine to use that as an argument to convince others. You have much better arguments: poor methods, insufficient evidence, lack of controls, etc. and none of those rely on personality.

Good point. I think people may confuse logic with believability.

I could propose in this comment a cure for cancer based on a perfectly sound a logical argument and my (lack of medical) credibility would have zero affect on the cogency of what I was saying.

But it does mean, you should probably not be convinced, or at least not send me all of your money to invest in my cancer research startup.

Also for some reason it's very easy to judge something as reasonable when we actually don't have any domain expertise. Not sure why, it seems built into most of us to feel natural.

I'm not going to give an inch on this. This isn't an issue of logic versus persuasion. It is logically valid to attack the credibility of an argument that depends in any way, implicitly or overtly, on the credibility or authority of its bearer.

The "ad hominem fallacy" is misused on the Internet probably more than it is applied correctly.

I don't think you have to give an inch. I'm agreeing it's legit to judge someone's argument based on credibility.

The reason is imperfect information. If I described here an actual, real, cure for all cancer, people shouldn't believe it because credibility is shit, it hasn't been clinically proven, and it might take 10 years to do so.

If I write in a solid proof for a millennium prize problem, you're probably going to be safe not worrying about my credibility at all because the truth will be known in pretty short order.

Usually the more uncertainty the more credibility has to be weighted.