Logical Fallacies

Almost everybody knows about the fallacies of logic, formal and informal, that are routinely used in arguments with denialists. While these fallacies aren’t perfect examples of logic that show when an argument is always wrong, they are good rules of thumb to tell when you’re listening to bunk, and if you listen to denialists you’ll hear plenty. I wish they’d teach these to high school students as a required part of their curriculum, but it probably would decrease the efficacy of advertisement on future consumers.

The problem comes when the denialists get a hold of the fallacies then accuse you, usually, of ad hominem! It goes like this.

Denialist says something wacky…
Commenter or blogger corrects their mistake…
Denialist says same thing, changes argument slightly…
Commenter or blogger again corrects their mistake…
Denialist says something even wackier, says it disproves all of a field of science…
Commenter or blogger, exasperated, corrects it and threatens disemvowelment…
Denialist restates original wacky argument…
Commenter or blogger’s head explodes, calls denialist an idiot.
Denialist says he won because commenter or blogger resorted to ad hominem.

The thing to remember about logical fallacies is that their violation isn’t proof or disproof of the validity of the opponent’s argument. Your opponent might just be an idiot, but ultimately right. Some people just don’t know how to argue or keep their temper. Logical fallacies are rules of thumb to identify when portions of arguments are poorly constructed or likely irrational. They are dependent on context, and aren’t really rigorous proofs of the validity or invalidity of any argument.

Further, some fallacies, like ad hominem are poorly understood, so when an opponent says you’re wrong because of this this and this therefor you’re an idiot, the poor victim of the ad hominem feels like they can claim victory over the argument. When in reality ad hominem refers to the dismissal of an argument by just insulting the person. Time and time again you see someone exasperated by the crank who won’t turn despite being shown again and again where their error is, and finally just call the guy an idiot. That’s actually not an ad hominem. That might be totally true and highly relevant to the argument at hand. Sometimes people are just too stupid or too ignorant to realize when they’ve been soundly thrashed, and true cranks will stubbornly go on, and on and on…

But that doesn’t mean the fallacies of logic aren’t useful as rules of thumb for detecting the BS. The ones you hear most are arguments from metaphor or analogy (prime creationist tactic), appeals to consequence (creationist and global warming denier), appeals to ignorance (all – see moving goalposts), appeals to authority (all), straw men and red herrings.

For instance, the classic creationist example of using the analogy of the mouse-trap to suggest “irreducible complexity” as a problem for biology. Fallacies let you dismiss this instantly by saying, analogies aren’t science pal, how about some data. Analogies are often helpful for getting concepts across, but you routinely see them used by denialists as evidence. And more frequently you see their analogies aren’t even apt. For instance the mouse-trap is perfectly functional as its constituent parts. It’s a platform, a spring and a hook, just because they’re not assembled doesn’t mean they’ve lost their function. They just can’t kill mice anymore unless you throw them with sufficient velocity at rodents. Similarly the watchmaker analogy, the jet airplane analogy, or when a few months ago I saw this endless silly analogy about arsonists and design. Uggh. Pointless. Don’t even bother, you see things like this being used to challenge actual honest to goodness data? You’re done. If you spend too much time piecing together looking for a method to the madness you’ll end up like our poor robot. He’s the mascot for logical fallacies.


Poor guy. One too many fallacies, now he’s broken.


13 responses to “Logical Fallacies”

  1. Here’s the link to my complaint about stupid claims of ad hominem. Bonus: Stupid Creationist all over the comments.

  2. One of the most frustrating things when you’re in a debate with someone is trying to explain just what is and isn’t a fallacy. If that person hasn’t studied some philosophy or logic, the subtle differences between a legitimate appeal to authority and a fallacious appeal to authority are often lost on them. Sometimes I just avoid pointing out fallacies if I know the person I’m talking to isn’t going to understand the difference between between a valid and an invalid argument. All they’ll do is try to pull the “I know you are, but what am I?” argument and accuse you of the same fallacy as soon as they get the chance, regardless of whether you actually committed the fallacy or not.

  3. This is a good example of a little knowledge being a dangerous thing. Typically, after they’ve had their noses rubbed in their own fallacies a few times, the serious blog/forum trolls will look up a few sources on the subject. Then, suddenly, they start accusing everyone else – often improperly – of constructing strawmen and making appeals to authority and engaging in ad hominem attacks and so on. This generally makes them even more annoying than they were before. From time to time I’ve even foregone a particular kind of logic-based rebuttal because it feels too much like I’m training them how to avoid obvious mistakes and thus be more effective at what they do. The last thing the net needs is more people who are good at presenting fundamentally flawed ideas in ways that take more time to refute.

  4. What always bothers me is that a mousetrap is not irreducibly complex in the least!

    Thus Behe is either (i) ignorant of this fact, or (ii) knows of this, and yet continues to use it as an example. So, he is either living under a rock and not interested in reading up on current literature, or simply a baldfaced liar.

  5. Mustafa Mond, FCD

    Almost everybody knows about the fallacies of logic,

    Very clever, starting out with an argumentum ad populum.

  6. Mustafa Mond, FCD
  7. tbell

    I’ve enjoyed your denialist deck of cards, and thought maybe someone should do the same for more general fallacies and bogus tactics. And actually instantiate it in a card deck, or key chain flashcards that you can keep handy when you are getting baffled with bullshit and bogus debate.

    Over the past two days I’ve been thinking about a problem that is almost the reverse of the problem of bogus tactics, that is, a straightforward delineation of the bases for legitimate (intellectually honest) disagreement and argument. I’ve never seen a really good one, though I’m sure it’s out there. A list that might go something like : disagreement about facts of the matter, what constitutes evidence for a fact, which facts are relevant, how much weight to give to certain facts, which interpretations are possible, whether a question is well formed, whether terms are being used by both parties in an identical fashion, etc.

    Also, I’d like to see a more in depth exploration of why bogus tactics seem to work, or sway an audience. Ad hominem is fairly straightforward. But why does ‘guilt or merit by association work’. E.g. ‘Your idea is bad because it is associated in some way with something else that is bad’? Another example ‘Why do people reject ideas that have implications that they dislike? At a simple minded level it could be just avoidance, but is there anything else to it? We often reason towards conclusions, selectively gathering evidence for or against. This is fraught with difficulty, but also can be efficient in many ways. Perhaps rejecting an argument because of it’s perceived implications is another form of this.

    Apologies if I’m being too cryptic, it’s hard to pack much into a blog comment. Anyway, I’m enjoying the your blog. Keep it up.

  8. Andrew Dodds

    Very clever, starting out with an argumentum ad populum.

    Clearly an attempt to poison the well..

  9. Pete Dunkelberg

    Here’s the KISS version.

  10. Torbjörn Larsson, OM

    I wish they’d teach these to high school students as a required part of their curriculum

    I know what you mean! Instead of free lessons in driving, rhetorics, argumentation or how to buy a decent apartment, they want to teach you such ‘useful’ stuff as a third language. “The rest life can teach you, we will teach you skills you need for your further education”. Yeah, right.

    I wish they’d teach these to high school students as a required part of their curriculum

    Awww, fer cute!

  11. divalent

    “The thing to remember about logical fallacies is that their violation isn’t proof or disproof of the validity of the opponent’s argument.”

    Um, actually, a fallacious argument *IS* an invalid argument. I think you meant that it not proof or disproof of their conclusions. It’s an important distinction, because pointing out a logical fallacy should (in an honest discourse) end the discussion until the proponent can rectify the error.

  12. Sometimes I just avoid pointing out fallacies if I know the person I’m talking to isn’t going to understand the difference between between a valid and an invalid argument.

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