Logic is not something that only Vulcans do on the television series, Star Trek. Nor, is it the invention of television writers. We can actually blame the ancient Greeks for both the word and the concept. Aristotle wrote one of the first books on the subject and laid the foundations for the discipline. So today, anyone can take courses at universities in logic.

It is a handy subject. It can teach us how to think. One of the aspects of the course that I found most enjoyable when I took it was what is called “informal logic.” Specifically, we spent a lot of time looking at these wonderful things called “logical fallacies:” common mistakes in thinking that lead people to erroneous conclusions.

Of course, most people don’t know about “logical fallacies” and so when you find out about them, you can bamboozle your friends, become a logic nanny, or you can unmask politicians and advertisers who seem to use them the way a fish drinks water.

There are, of course, bunches of these logical fallacies. Whole books have been devoted to their analysis and even the chapter in my logic book was rather long. Said chapter concluded with a bunch of exercises where quotations from politicians and others were given for the student’s enjoyment and enlightenment—the hope being that having read the chapter, we could now identify the specific mistakes that had been made and give them nifty, impressive sounding Latin designations like argumentum ad hominem.

I will refrain from using fancy Latin words, however, and give more meaningful, plain English names for some of the most common errors of thought to which human beings are subject. Learn these, and annoy your friends with them, or better yet, laugh at politicians next time there’s an election.

So what is an argumentum ad hominem? Why, that’s just an old fashioned “insult the guy.” If you can’t refute him, hit him. For instance: your friend was right when he points out that you are mistaken: the capital of California is Sacramento and not San Francisco. Don’t put up with it. Instead, explain to your friend that he’s ugly and his mother dresses him funny. Your political opponent whups you with facts and figures? Announce that he’s an insensitive rich guy. Your buddy beats you in basketball? Say mean things about his girl friend.

Notice that the nature of all logical fallacies is well illustrated by this particular one: they are irrelevant arguments. They distract from the actual issue at hand. In that sense, logical fallacies are like a stage magician: he depends on slight of hand and misdirecting your gaze. “Pay no attention to that man behind the curtain!”

When my parents warned me to do my homework or they’d put me in time out, they were making use of the next logical fallacy and perhaps an equally common one: “the threat of force.” Obviously, if I tell you that you need to do what I’ve told you or “I’ll beat you senseless,” though my argument will perhaps get you to perform, I have not convinced you to behave by reason. My argument is irrelevant to the truth or falsity of what I’ve said. “The sun is the center of the universe” followed by the threat that to fail to accept this nugget will result in the loss of employment, or that you’ll suffer a heresy trial, or that you’ll be ostracized and ridiculed, does not prove that the statement is true. It has nothing, really, to do with whether the information is right. But by golly you’ll get a lot of people to agree with you when you threaten, whether explicitly or implicitly.

Have you ever had someone tell you something like, “Purple flowers eaten when the moon is full will ensure rain the following week?” And then when you question whether there’s any proof to such an assertion, all you get back is, “no one’s ever proven me wrong.” This is what is known as “an appeal to ignorance.” It is a favorite of crackpots and those who sell snake oil. “Brussels sprouts are the spawn of Satan. This statement has never been refuted.” Such an assertion proves nothing at all, of course. The inability to refute something is not a demonstration that it is true. Likewise, if I were to say, “String theory is false because it has not been proven true,” my statement is just as invalid and illogical. Failure to prove something true does not mean it isn’t. Just because Galileo couldn’t prove to his inquisitors that the Earth went around the sun, does not mean that he was wrong. It just means he couldn’t prove it. The truth or falsity of something is not dependent upon our ability to demonstrate it.

No doubt you’ve heard advertisements along these lines: “Four out of five dentists” or “56 percent of those surveyed” and so on. This is an “appeal to the multitude” or what’s sometimes called an “appeal to popularity,” like the amusing bumper sticker, “Eat lamb. Ten million wolves can’t be wrong.” But of course it is obvious, once one thinks about it a moment, that simple popularity does not prove the truth or falsity of a concept. Just because the majority of Germans during the Nazi era thought Jews should be deprived of their civil rights, does not make their position correct. Just because the majority of southerners, prior to the Civil War, believed slavery was a fine institution did not make it so.

Likewise, just because you can demonstrate that a famous actor believes that a particular brand of diet soda is the best, does not mean that I’m going to like drinking it. This is known as an appeal to authority. “Of course the Red Sox will win this year. My dad said so.” No disrespect to your father, but just because he says so doesn’t make it so. Telling me that your position is correct because a famous politician, scientist, preacher, or other authority says it is, does not prove you’re correct. You’ve merely given your position a character reference. But unless you can argue your position with facts and figures to support it, all the character references in the world won’t rescue you. After all, the Prime Minister of England, Neville Chamberlain, said of Adolph Hitler that he was “a man that could be reasoned with,” that he “could be depended upon,” and then he waved the treaty in the air and announced that with Hitler’s signature, it meant “peace in our time.” Nevertheless, Hitler was soon bombing England, among other even more reprehensible things.

And finally, one of my favorites, is what can be called the “You too” argument. We see politicians using it frequently, and we’ve seen totalitarian nightmare regimes make use of it too. In the old Cold War days it would go something like this. We’d criticize the Soviet Union for starving a million Ukrainians while marching the rest into the Gulag to serve as slave laborers, and then the Communist thugs would turn around and say, “Well, just look at how you treated the Indians.”

Or politician A will criticize politician B by saying, “My opponent cheated on his income tax and cheated on his wife. He’s a cheater by nature.” Politician B responds with, “My opponent has no room to talk. He’s been caught shoplifting from the neighborhood Walmart and here’s a copy of his mug shot.”

And of course the problem with this is quite simple. Say I criticize you for dropping your neighbor into a giant blender and serving him up with fava beans and a nice Chianti. Then you retort by telling me I have no room to judge, seeing as how you saw me holding up the local Savings and Loan last Tuesday.

Consider. Does my reprehensible robbery make it okay for you to consume your neighbor? Probably not. It is irrelevant to the criticism I’ve leveled. No matter how severe my mistakes, they have no bearing on yours. Nor do they suddenly make you virtuous. My boss will not take kindly to me if I point out how he has a lead foot, while he’s chewing me out for losing the Jones account. Obviously, his lead foot has no bearing on my incompetence, now, does it?

So the key in all of this logic stuff is to keep your eye on the ball and always ask yourself the very simple question: is this relevant to the matter at hand? If it’s not, then it is illogical. Simple as that.

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About R.P. Nettelhorst

I'm married with three daughters. I live in southern California and I'm the interim pastor at Quartz Hill Community Church. I have written several books. I spent a couple of summers while I was in college working on a kibbutz in Israel. In 2004, I was a volunteer with the Ansari X-Prize at the winning launches of SpaceShipOne. Member of Society of Biblical Literature, American Academy of Religion, and The Authors Guild
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