The Myth of Common Sense

How many times have you heard someone say, "It's just common sense"?  I just heard it myself (well, read it in an e-mail) two days ago, and it was in relation to something that I might argue wasn't really common sense at all—at least, not beforehand.  With the benefit of hindsight, it became common sense.  (If you're inordinately curious, it had to do with how hot a playground surface could get on a cool day.  Pretty hot, as it turns out.)

Right now, as I write this in late June 2011, if you google "it's just common sense," you get the following things that are supposed to be common sense:

• Domestic drilling for oil
• Creation science (I think—the post wasn't entirely coherent)
• The necessity of broad-ranging budget cuts
• Wearing a bicycle helmet reduces the risk of injury
• The use of backscatter scanners (so-called "naked X-rays")
• Avoiding texting while driving
• Essentially any Republican viewpoint on fiscal policy
• Showing discretion on social networks
• Allowing schoolteachers to bring guns to class (!)
• Using alternative medicine

Those are just the first ten hits that made an assertion that something or some position was "common sense."  I ignored any example that used the term in an ironic sense (most notably, "Repeal child labor laws?  It's just common sense!"), or were talking directly about common sense.

Now, one thing I expected was that there would be a split between things that were asserted to be common sense in a descriptive way (that is, people do commonly agree on them, or would if they were asked), and those that were asserted to be common sense in a prescriptive way (that is, people should agree on them).  And indeed there is, but the split was fairly unbalanced: I'd say that out of the ten hits I listed above, just three—the bicycle helmet one, texting while driving, and discretion on social networks—were even close to the descriptive sense, and the bicycle helmet one only alluded to common sense to set up the contrasting finding that apparently, it doesn't reduce the risk of injury.  (Very interesting, by the way.  But a post for another time.)

The remainder were all prescriptive; in general, they even conceded that a large segment of the population—be it liberals, non-religious people, gun-control advocates—were opposed to their viewpoint, but they then went on to say that these people were mistaken, and they were mistaken because they went against common sense.  In most cases, they don't really explain why their viewpoints were common sense; it was enough to say simply that they were.

And that demonstrates the appeal of saying that something is common sense: It removes the burden of proof from the person making the assertion, and places it on anyone who disagrees with it.  Essentially, it abdicates any responsibility for backing up your position.  More than that, it demeans anyone who disagrees, as they obviously lack common sense (whatever that might be).

Granted, it's always been a bit hazy exactly who has the burden in any particular case.  The negation of an assertion is, of course, another assertion, so who really has the burden of proof?  A convenient rule of thumb is that anyone who goes against the conventional wisdom position (the descriptive common sense, basically) assumes that burden, but there are, I'm sure, plenty of exceptions to that.  But I argue that in any borderline case, where there's some dispute as to who has the burden of proof, both sides should assume that burden.

So when someone writes that something is "just common sense," it almost always turns out (and I'm being as generous as I can here) that they don't exactly know why they hold their position.  Or won't say.  Or it's just too much trouble to actually work out and explain what their position is.  To which I'd say, "Well, then, why are you wasting your time explaining your common-sense position?"

To its credit, the bicycle helmet post actually points this out.  From Doug's Darkworld:

"It’s just common sense" is probably one of the most seductive and deadly false arguments out there. When someone says "it’s just common sense" what they are really saying is "reality conforms to my idea of what makes sense."

I would say there's other cases, but that is a big reason that people say something is common sense.  It puts me in mind of a point made by Michael Shermer.  Shermer's a skeptic of possibly the most compelling kind: a recovering occultist (an anti-skeptic, if you will).  He wrote a book in 1997 entitled Why People Believe Weird Things; he updated it five years later, most significantly including a new chapter entitled "Why Smart People Believe Weird Things."  In it, he argues the following thesis: Smart people believe weird things because they are skilled at defending beliefs they arrived at for non-smart reasons.

I can't emphasize strongly enough what a transforming revelation that was for me.  For much of my life, I'd encounter people holding what (to me, at least) appeared to be some kooky position or another, and my reaction was nearly always something along the lines of "How can you possibly believe that?"  And that was a rhetorical question; I wasn't really interested in how they came to believe that, I just wanted to point out that it was a nonsensical position.  As you might expect, I eventually came to realize that most people didn't particularly take kindly to that sort of question, so I stopped saying it.  But I still thought it.

Shermer's thesis, however, made me start asking that question again, but internally, and this time at face value: Why do they hold that position?  It's very often not for the reason they espouse.  (For instance, most of the common sense cases, I pointed out, are not in fact commonly held.)  Maybe it's because of their own personal experience; people tend to overvalue personal experience.  Maybe it's because of their religious or cultural upbringing.  Or maybe it's a position that has to be taken in order to avoid cognitive dissonance with something that they've done.  It's an interesting intellectual exercise, and sometimes I can work it out without coming straight out and asking them, "Well, why do you think it's common sense?"

But the other lesson is important, too: When someone says something is common sense, and that you should act in such-and-such a way because of it, it's vital not to adopt that common-sense attitude, if you don't already agree with it.  It can be surprisingly compelling, if you're not careful (after all, who wants to be demeaned?), and you may sooner rather than later find yourself espousing the same position, seeing as it's "just common sense."