The bullshit detection kit - Michael Shermer

Logical Fallacies 101: Argument from authority

Argument from authority (Latin: argumentum ad verecundiam) is a fallacious type of argument where A argues that a proposition is true on the grounds that B says that it's true. B may or may not be an authority on subject S, but A will always consider him to be.

Such arguments take the following form:

P1: B is an expert on subject S.

P2: B claimed X in subject S.

C: Therefore, X is true.

It may seem strange that we have no valid reasons to be certain about what B says. After all, that's why he is an expert, right? Right, but that does not mean anything regarding the truth of his claims. As with the previous fallacy, claim X's soundness cannot be based on what B, or the majority, believes. 

It may be that, in most cases, what Stephen Hawking says is true. But the argument "Stephen Hawking said that black holes behave in way X" is no more true than replacing "Stephen Hawking" with any other person. What is true though, is that since Stephen Hawking is an expert on the field, and we assume that he bases his theories on well worked-out models, and since what he said in the past was true (inductive reasoning), we are justified in testing his theories and not somebody else's. Whether theories are true or false, however, has nothing to do with who proposed or thought of them.

"So you are saying that we're not justified in believing the astronomer and not the anthropologist or the economist when she says that we have good reasons to believe that Planet 9 exists?", you may ask. Ofcourse we are justified. But what we must realize is that that carries a probability of error. Less if the anthropologist or the economist were to say the same thing, but it still does.

In this case, we can only be certain if we observe a body, that behaves like Planet 9 should, according to the theory, and based on our current models, is defined as a planet.

What people say, no matter how much expertise they have, is just considered a probability. Not a certainty. 

Logical Fallacies 101: Ad hominem

Being an atheist, secularist, and humanist society, DASH is committed in using reason when developing arguments. Reason differs from belief in the sense that it is a secure way to truth - or how philosophers would call it: 'the way things are'. And, as the Great Tyson (Neil, not Mike - though he is also great) said: "'The good thing about science is that it's true whether or not you believe in it."

However, we all sometimes fall into the trap of committing logical fallacies when arguing, fallacies which may convince but they are not based on firm sound grounds. DASH will weekly present one logical fallacy in an attempt to promote arguing with reason and developing sound arguments.

Ad hominem fallacy



Ad hominem is Latin for "to the person". It is a personal verbal attack to the person making an argument, rather than to the argument itself. Person B presents a fact about person A that is supposedly related to the argument A is trying to make, and rejects A's argument on that particular fact. 

The structure of the fallacy is this:

1. Person A makes claim X
2. Person B disregards the claim and attacks person A.
3. Thus, claim X is false.

The reason this is a fallacy is that any fact about A is unrelated to claim X. Claim X is or is not true, irrespective of who is the person arguing for it.

A different form of this fallacy is the circumstancial ad hominem. This is an attack on the person making a claim, on the grounds of that it is in his own interests to make a claim.

Example:

1. Person A: Decreasing the interest rate would be a good thing for the economy.
2. Person B: Ofcourse you would say that. You are a banker! And definitely bankers are expected to promote such views.

A's argument's truth is irrelevant to any fact about A; in this case his job. Even if A supports that claim because he is a banker, B should attack the argument using economic, financial, or other relevant, terms. The key is that in such terms, B is able to objectively criticize A's claim.

"Are ad hominem arguments always fallacious?" you may ask. Yes, in most cases. However, there is an exception. The above cases are cases in which person A was making an argument. A's credibility was irrelevant. In cases of a statement of fact, however, that is when A is making a testimony, A's credibility is of utmost importance and needs to be assessed.