The Internet is teeming with crazies, jerks, and blowhards; and in online forums, debaters are full of passionate intensity. Peruse the comments area on any popular blog, and you’ll find more irrational rhetoric than you can shake an encyclopedia at.
What separates rational thought from bogus blather is logic. Unfortunately, sound logical thinking is a learned skill that’s rarer than we might hope, and it’s not the same as so-called common sense.
What’s a Fallacy?
A fallacy is a logical error. Logic is a method of reasoning in which the statements used to support a conclusion must be true in order for the conclusion to be true. When the statements used to support a given conclusion do not actually work together to support the conclusion, we call this a fallacy.
It’s worth bearing in mind that a statement can be fallacious even if its conclusion happens to be true. What differentiates sound reasoning from a fallacious argument is not the accuracy or inaccuracy of the conclusion it reaches, but its fidelity or infidelity to the principles of logic.
Using or falling for fallacious reasoning is by no means a sign of stupidity. Lots of smart people inadvertently use or get taken in by irrational arguments from time to time–through lack of attention, lack of understanding about how logic works, or the simple fact that human psychology is riddled with weird idiosyncrasies that make us susceptible to misunderstanding. And of course, some people deliberately use fallacious arguments because they know that others will fall for them.
Here are ten of the most common logical fallacies that you’ll find online.
Bald Assertion
The iPod is the best music player on the market.
Oh, really? Prove it.
PC World’s forums are chock-full of bald assertions like the one above. What makes this kind of statement fallacious is the sheer absence of evidence offered to support it. Many online commenters don’t bother to back up their claims with facts, and this makes assessing the reasonableness of their assertions difficult. That being the case, it’s hard to fault someone for dismissing such a statement out of hand–even if it’s true.
Think Opera is the best browser around? Okay, fine. But unless you can explain why you think so, you offer readers very little reason to care about or come around to your opinion.
A good rule of thumb for avoiding this problem in your own online posts is to consider how controversial your statement is likely to be. If you suspect that reasonable people might need a little convincing, it’s best to offer additional reasoning and to refer to supporting evidence.
Ad Hominem
You obviously don’t know anything about Windows, because you’re a Mac fanboy.
Don’t feel like making an honest case to refute a statement you don’t like? Why not just attack the person directly? When you target the person you’re arguing against instead of focusing on the content of their argument, that’s called an ad hominem fallacy. “Ad hominem” literally means “to the person,” and it’s one of the most blatant fallacies you’ll find anywhere.
Another common form of ad hominem argument–and one commonly used against tech journalists–goes something along the lines of “You can’t trust anything this guy says, because he’s been paid off by Microsoft/Apple.” Unsurprisingly, whenever we say something critical of one company, we’re accused of taking bribes from the other.
Genetic Fallacy
That information came from Wikipedia, and we all know Wikipedia can’t be trusted.
Like the ad hominem approach, the above argument ignores the content of a statement and puts all of its energy into attacking the source. We call this a genetic fallacy because it suggests that information may automatically be untrue simply because of where or who it came from. Of course, that’s baloney. To prove that a given statement is either factually wrong or illogical, you have to address the content of the statement itself.
No True Scotsman
Mike: No Linux user would say something like that.
Billy: I’m a Linux user.
Mike: No real Linux user would say something like that.
The No True Scotsman gambit is cheesy bit of rationalization that draws an imaginary distinction between one kind of thing and a nonexistent “true” version of that thing, usually as a way of avoiding admitting a mistake.
In the example above, Mike modifies his original false statement with a qualifying word (“real”) that makes the assertion subjective rather than objective. Whereas the claim “No Linux user would say something like that” is disprovable by a single exception, the claim “No real Linux user would say something like that” allows Mike to avoid acknowledging that Billy counts as such an exception: In fact, Mike’s revised wording amounts to saying that by contradicting the original assertion, Billy automatically disqualifies himself from being a “real” Linux user. In online forums, many people skip the first step and jump straight to the No True Scotsman fallacy. It saves time, but it’s still wrong.
The Straw Man
Dan: Netbooks can be easier to use than full-size laptops when you’re traveling, because they’re lighter and fit better on an airplane tray table.
Want an opponent who’s easy to beat up? Build yourself a straw man–he doesn’t even have a brain. The straw man fallacy is irritating because it misrepresents and trivializes the opposing view. In the example above, Jimbo alters Dan’s argument to make it patently false, and then attacks the weaker argument instead of addressing what Dan actually said. Jimbo is ignoring the fact that Dan was talking a specific circumstance in which his statement might be true. Jimbo is a jerk.
Argument From Ignorance
I’ve never seen any evidence that disk defragmentation speeds up PCs, so it’s clearly a waste of time.
If you don’t know something, it’s hard to draw a reliable conclusion about it. This is the core weakness of the argument from ignorance. In the above example, the arguer draws a conclusion based on a lack of evidence–which is pretty much the opposite of rational inference. Not only is this guy reaching a conclusion based on not having seen something, but it’s unclear whether he ever tried to gather the information in the first place. It’s the same fallacy as saying “I’ve never seen duck-billed platypus, so there are no duck-billed platypuses.” Of course, your personal experience of something is by no means irrelevant to your assessment of it: Never having seen a Gorn except on Star Trek is a data point that you can legitimately consider in assessing whether Gorns exist. But your personal experience isn’t the sole arbiter of what is real. As a matter of logic, we can’t use our own ignorance (or nonexperience) as dispositive proof that an assertion is true (or false).
The Bandwagon
Almost everybody uses Windows. It’s clearly the best OS around.
Also known as an appeal to popularity, this fallacy equates popularity with value. By this reasoning, the Big Mac is the best hamburger on earth and Reader’s Digest is the best magazine. It’s possible for a best-selling product to be the highest-quality one as well, but popularity doesn’t automatically mean excellence. If you want to prove that your favorite operating system, phone, or other media player is better than the competition, try talking about its features.
The Hot Hand
Apple has released a lot of great products lately. Its next Apple gadget is bound to be great.
Depending on who you ask, the hot-hand fallacy gets its name from the sports world or from the gambling world, where players tend to believe that a series of back-to-back wins indicates a “hot streak.” There’s nothing fallacious about acknowledging a run of successes, but a past win does not guarantee a future win, any more than a run of ten heads on consecutive flips of a normal, balanced coin makes heads (or tails) more likely on the next flip.
The above example from the tech world is a fallacy because it asserts that a particular future outcome is a certainty, based entirely on past performance, without offering any substantive support for the expected result. But a given product succeeds or fails (for the most part) on its own merits. And while having a talented design team undoubtedly strengthens a company’s chances of putting together something great, the argument used in this example doesn’t focus on that legitimate consideration at all.
Like every other decades-old business, Apple has had some misses as well as hits. The tendency to ignore the strikeouts and remember only the home runs is an example of a well-known psychological effect called confirmation bias.
Argument From Authority
Leading security experts say that every computer should run a complete security suite.
Regrettably, no one has the time, patience, or inclination to become a bona fide expert in every field of study. To compensate for this limitation, we instinctively seek out trusted sources in search of reliable information. But sources are not equally reliable, and some are just plain bunk.
Furthermore, even normally reliable sources get things wrong sometimes, and it’s not uncommon for good information from a reliable source to be quoted out of context by some blowhard in an online forum. Since supposedly authoritative sources are subject to error or misquotation, argumentative appeals to authority don’t irrefutably prove a given conclusion.
Hasty Generalization
I tried Linux once, and it was hard to use. Linux is too hard to use.
We humans make sense of our world by making educated guesses on the basis of the information or experience we happen to have. In psychology, these simple rules of thumb are known as heuristics, and we all seem to be wired to employ them whenever we’re faced with uncertainty. Without heuristics, we’d find ourselves paralyzed by doubt and unable to make useful judgments about how to spend our time, money, and energy. And at a simpler level of generalization, we might never draw a useful conclusion from the fact that every time we stick our finger in a fire it gets burned.
The downside of heuristic decision making is that it can lead to hasty generalizations like the one above. In this example, the speaker uses a single experience with Linux to draw an blanket conclusion about Linux. It could be, however, that this person tried one of the more obscure or less intuitive distributions of Linux, or that he tried one with an interface he was unaccustomed to and didn’t take the time to learn it. Though we can’t fault this person for deciding not to bother with Linux after his first experience, the generalization that the hundreds of Linux distributions in existence are all just like the one he tried is fallacious.
The hasty generalization belongs to a category of logical errors known as inductive fallacies, all of which involve making unwarranted assumptions on the basis of limited information.
A Note About Arguments
For many of us, the word “argument” is fraught with negative connotations. It implies fighting and disagreement, and it conjures up images of angry people bickering with each other. But in logic, an argument is merely a set of statements that support a particular conclusion. In this view, arguing is simply the act of saying something meaningful.
It’s almost impossible to state a reasoned opinion about anything without presenting some sort of argument. So you needn’t think of arguments as bad things to be avoided. Whether our online interactions are good or bad hinges on how we argue, not on whether we do.
In any debate–online or in person–it’s important to assess honestly the facts and arguments we encounter, and to try to understand what others are actually saying. Most flame wars stem from a basic failure to consider the opposing view rationally, or from an assumption that our opponents can’t possibly be right (or that we can’t possibly be wrong).
If we let rein in our egos and consider the facts and reasoning presented to us, we stand a far better chance of persuading others or–just as important–discovering our own errors. Either way, we win.
Food for Thought
Critical thinking is a learned skill, and it doesn’t always come easily, but it’s well worth practicing. Armed with an understanding of how logic works (and how it doesn’t), we’re less likely to be persuaded by nonsensical arguments, even when they’re draped in authoritative quotes and appeals to popularity. Better still, developing sound reasoning skills gives us the tools we need to have more useful and interesting discussions about the things that matter to us.
In this article I’ve touched on only a handful of the many logical fallacies that plague daily conversation both online and offline; there are many others. Fortunately, the Web contains some excellent resources that offer plenty of fodder for your critical mind. Here are a few good sites to peruse:
Wikipedia: This publicly edited encyclopedia takes more than its share of (often fallacious) abuse in the press, but as a reference for critical thinking and logic, it’s tough to beat.
Nizkor: Dedicated to countering the irrationality of Holocaust denial, Nizkor is home to an excellent database of logical fallacies.
LogicalFallacies.info: Simple and direct, this no-frills site offers an extensive, well-organized list of logical errors.
The Skeptics’ Guide: Created by the New England Skeptical Society, the Skeptics’ Guide to the Universe is a popular podcast about science and critical thinking. Its companion podcast, Skeptics’ Guide 5×5, offers 5-minute explorations of common logical fallacies and misconceptions.
Robert Strohmeyer is a senior editor at PC World. He tweets as @rstrohmeyer.