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Comment by swivelmaster | Hacker News Reader

Pointing out that someone is not an expert at something is not an ad hominem.

Arguing against someone's position by simply stating (truthfully or not) that they are not an expert is textbook ad hominem.

Come on. Evaluating the merit of a source is critical thinking 101.

As, and “X is not an expert in Y” is a valid response to an argument resting on X’s authority, but not otherwise a counterargument.

Perhaps it more closely resembles an appeal to authority or appeal to accomplishment.

This isn't an appeal to authority though. That would be saying, "I'm right because I'm the expert." This is saying, "I don't trust you because you're not an expert." That's not a logical fallacy.

Even experts in adjacent or overlapping fields are suspect. I'm a flight instructor. I teach in airplanes. Would you believe what I have to say about helicopters? You shouldn't. I don't know jack about them.

If you told me I had low tire pressure I wouldn't ask if you're a mechanic. I would look at the tire myself. If I was unable to use a pressure gauge due to a lack of my own expertise, I still wouldn't be in a position to question your observation about the tire based upon your credentials alone. The best counter argument I could mount would be, "It looks full to me" or "I checked the pressure this morning". Dismissing your observation because you are a flight instructor, not a mechanic is exactly what an appeal to authority is.

He’s either correct about your tire pressure or he’s not. You’re right about that part. That’s as far as the purely logical bit can go—then you get to economics: Should you spend the time and energy to give his claim credence? Your example is poor because tire pressure is an expertise the average person you’re likely to come into contact with likely possesses. This is not so of, say, the epidemiological issue in question.

If you picked up a member of an Amazonian tribe who had never seen a car before, are you going to worry about the tire if he claims the tire pressure is low? Well, sure, it’s easy enough to check. But what if it was $500 to check? No. I don’t think you would.

Yes, I attempted to cover that eventuality in my example. Let's say I am not qualified to examine the tire myself and someone who's ability I also doubted made an observation.

Here's what I wouldn't do: prejudicially dismiss the tribesman's opinion, citing his lack of authority on the topic.

Even if we accept the premises of an appeal to authority, it would follow that one would have to also be an authority on the topic before he could determine the authoritativeness of another speaker. How can you evaluate the authority of a speaker, if you yourself are not an 'authority' on the topic?

Even if you are an authority, does this status render you infallible?

No, I'm afraid the entire premise is ridiculous.

> Here's what I wouldn't do: prejudicially dismiss the tribesman's opinion, citing his lack of authority on the topic.

Even if you wouldn't in this particular case, you can't possibly function in the world if you eschew questions of trust completely. You'd basically have to prove everything yourself.

> Even if we accept the premises of an appeal to authority...

An appeal to authority is claiming something is true because an authority said it. The inverse of that would be that something is untrue because no authority said it. No one is claiming that to be the case and even if they were, that wouldn't make it an appeal to authority. In any case, this is a question of credibility (i.e., trust).

> ...it would follow that one would have to also be an authority on the topic before he could determine the authoritativeness of another speaker.

This doesn't follow at all. I am not an expert on tires, but I can understand that someone who has never even seen a tire is also not an expert on tires.

> Even if you are an authority, does this status render you infallible?

No. Of course not. But it does make you a more credible source of information in your field of expertise.

There's a difference between dismissing someone's objection solely for lack of credentials (an appeal to authority) and valuing the opinion of an expert.

The former is absolute, the latter allows for other factors of consideration.

What counter-argument are you referring to? I only see a comment that points out the author isn't an epidemiologist, which seems relevant to an epidemiological prediction.

This is a good example of why "ad hominem" is one of the worst arguments you can try to use against something.

In actual human discussion, pointing out that someone is making claims about something they don't know anything about is the very basis of common sense. Trying to make this out to be a logical fallacy only shows how useless that label is.

The problem becomes how you quantify your opponent's knowledge from a subjective position.

How can you prove that they don't know what they are talking about without disputing the points they have made?

You must attack the argument, not the person.

No, you really don't. This isn't a mathematical proof. This isn't a formal debate. This is regular, common-sense discussion.

Pointing out that a guy who is not an expert in a field is making claims that go against the actual experts in that field is a perfectly reasonable argument, and ignoring it is intentionally blinding yourself.

From the Wikipedia article on ad hominem arguments:

"Ad hominem (Latin for 'to the person'), short for argumentum ad hominem, refers to several types of arguments, some but not all of which are fallacious." [Emphasis added]

In particular, pointing out that someone is speaking outside of their area of expertise is a logically valid ad hominem argument.

"He wants you to believe that green is the best color of M & M, but his business went bankrupt," is an ad hominem argument.

"He trains parakeets, so I don't find him a credible source of dog behavior" is not.

"He trains parakeets, so you should not believe his position that the dog salivates because the bell rings" is.

The trouble with your example is that it conflates common knowledge and expert opinion.

No one would question a parakeet trainer now if he claimed dogs respond to Pavlovian conditioning, because it is common knowledge that dogs respond to this type of conditioning.

However, if Pavlov had been a parakeet trainer and simply asserted dogs respond to Pavlovian conditioning rather than discovering and researching it, it would not have been an ad hominem argument to state he doesn't know what he's talking about... because he didn't until he studied and researched it.

Arguing against their position by saying that they kick puppies is textbook ad hominem. Saying that they are not an expert isn't a strong argument, but it is a valid criticism.

It isn't the same as invalidating the argument. It doesn't approach the substance of what was presented. There is no substance to the objection.

Assertion: "That apple will fall on your head"

Appeal to authority: "You're not a physicist! Show me your PHD."

In the situation where the argument being put forward relies on the explicitly or implicitly stated expertise of the orator - such as an article which says "Take heed of my opinion of the important medical factors here, for I am a doctor" - contending that said orator doesn't have that expertise is entirely valid, and not ad hominem. Ad hominem is such when the attack on the orator is orthogonal to their argument.

It does not disprove the claim, but it does put it in perspective, and warn that you shouldn't take the claim with fully understanding it, and, preferably finding reputable analysis or rebuttals.

It's not an informative comment criticizing the author's credentials. It a drive-by insult.

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