Yesterday I was listening to an old Bill Craig debate on the resurrection (because what else are you going to listen to when washing dishes?) when I heard an audience member in the Q&A accuse Craig of argumentum ad populum … and then have the gall to start chanting “Shame!” Geez man, if you want to protest something get a “We are the 99%!” placard and hop a bus to Wall Street because you don’t belong in a debate hall. Shame indeed.
What really bothers me is the inane appeal to this logical fallacy which is, sadly enough, a terribly frequent occurence. An argumentum ad populum is an informal logical fallacy in which one seeks to establish the truth of a proposition by appealing to common opinion. Consider this conversation outside a 7-11 back in the year 1978:
Wade: “Al, that cigarette’s going to kill you.”
Al (blowing smoke in Wade’s face): “Gimme a break. Everybody smokes.”
Clearly Al’s rejoinder is spurious. Even if everybody smokes, it doesn’t follow that smoking is harmless.
Our brash questioner didn’t explain how he thought Craig had committed the argumentum ad populum, but I can think of two possibilities. In the first point Craig observed that most New Testament scholars recognize that the New Testament text has been established to 99% accuracy. In the second Craig observed that most New Testament scholars accept a set of facts about the empty tomb, post-resurrection appearances and resurrection belief of the early Christians. Are these really examples of argumentum ad populum?
No, it isn’t. We need to understand that the fallacy skates closely to a wholly rational, justifiable form of reasoning. Consider the fallacy of appealing to popular belief as the equivalent of a counterfeit Burberry bag, while the legitimate appeal to common belief is a real Burberry bag. Now imagine if you went up to some rich suburban lady in the shopping mall and said “Yer bag is counterfeit!” Not only would you be a jerk, but you’d also be a fool for assuming that every bag with a Burberry design is fake. The key is to recognize that many of the bags are genuine from the factory. So you better be sure you can tell the difference before you start pointing fingers.
The same goes for appeals to consensus. Let’s return to Wade and Al’s conversation in progress:
Al: “How do you know that smoking is bad for you?”
Wade: “Well, for starters a new survey of medical doctors published in the New England Journal of Medicine found a clear consensus of well over 95% of physicians accept that the link between smoking and cancer and heart disease is ‘clear and unequivocal’.”
Al (sticking out his tongue with disdain): “Pfft. That’s a logical fallacy dude. Just because a bunch of doctors say x don’t make x true.”
Al’s right. A bunch of doctors saying x don’t make x true, just like a bunch of people smoking don’t make smoking healthy and a bunch of people reading their horoscopes don’t make astrology true. But that’s to miss the main point. As we navigate the world we regularly defer to consensus opinion in forming our beliefs and courses of action. Everything depends on whether we have a reason to think that the consensus would be informed about the matter on which they’ve formed a consensus, and whether we have no defeaters to accepting this consensus.
A consensus of New Testament professionals on certain facts of ancient history is significant just like a consensus of doctors on the harm of smoking or a consensus of climatologists on the origin of climate change. Forming beliefs based on consensus opinions of this type is an excellent basis for rational belief.
Craig was fully able to explain why the consensus exists (indeed he did so in his debate, a fact lost on the clueless questioner), but even if you are unable to explain why experts hold a particular consensus you can still reasonably accept the consensus. When most physicists develop a consensus on the properties of the Higgs boson, believe me I’m takin’ their word for it. And if most meteorologists tell me it’s going to rain tomorrow, I’ll take my umbrella, even if I can’t follow the complex computer models that led to their forecasts.
So when we hear somebody appealing to a consensus in support of a particular conclusion, we should ask ourselves (1) do I have reason to think this consensus would have an informed opinion on the question? and (2) do I have any reason to distrust the consensus? And also keep in mind that there is a range of degrees of assent to the truth of a proposition. A consensus may be sufficient for you to conclude that p is more likely than not-p, but not much beyond that. Or it may be sufficient to yield a very high conviction about the truth of p.
Keep those points in mind and hopefully you’ll avoid the informal logical fallacy of appealing errantly to informal logical fallacies.