An idea can be truly “common sense” – both common and sensible – yet not be true. You don’t catch a cold from getting cold, and a popular majority may not be a legislative majority. (More)

Common Sense Problems, Part II: When Common Sense is False

This week Morning Feature considers the problems with “common sense.” Yesterday we began why many ideas are called “common sense” yet in fact are not both common and sensible. Today we see some ideas that are both common and sensible, yet are still false. Tomorrow we’ll conclude with ideas that defy common sense, yet are still true.

“Bundle up or you’ll catch a cold!”

The idea that getting cold gives you a cold is truly “common sense.” Most of us were told “Bundle up or you’ll catch a cold!” at least once or twice as we prepared to go play in the snow. Some of us may have said that to our children. It’s an example of an old wives’ tale, a lesson passed down through generations, and the myth is common enough to be listed at CommonCold.org, BabyCenter.com, and Vicks.com.

The idea that you catch a cold from getting cold also makes intuitive sense. People in cold climates more often catch colds in the wintertime. If that weren’t enough intuitive evidence, consider that a runny nose is a common cold symptom and cold weather makes your nose run. Those two facts – and both are true – seem to confirm the common sense notion of “Bundle up or you’ll catch a cold!”

“Coincidence does not infer causality”

But intuition can lead us astray. Yes, people in cold climates catch more colds in the wintertime: but not because they get chilled outside. It’s because more of them spend more time inside, passing around the viruses that cause the common cold. As for cold weather sniffles, that’s respiratory biology and basic thermodynamics, as Dr. Andrew Lane explained to NPR:

One of the main functions of the nose is to warm and humidify the air that we breathe so that when it reaches your lungs, it’s nice and conditioned. And in order to do this, the nose has to add some moisture to it.

When it’s very cold out, the air is usually dry as well, and the nose is really working overtime to add some fluid. And there are reflexes that are in place that allow the nose to increase its fluid production. And if it really makes a lot of fluid, then it starts to run out of the end of your nose.
[…]
Now the other side of it is the physics part. [When you see your breath on a cold day] what’s happening is that the warm air that you’re breathing is condensing in the cold air, so you see it as little droplets of water. And that’s because cold air can’t hold as much moisture as warm air. When you breathe that air back out, it comes to the very tip of your nose where the nose is cold and that fluid is going to recondense onto the surface of the nose and that will also run out.

This highlights one of the most common logical fallacies: correlation does not imply causation. Even scientists must work to design experiments that distinguish coincidence from cause, and guard against jumping to conclusions. While “Bundle up or you’ll catch a cold!” truly is common sense … it’s not true.

“A majority of Americans agree!”

We read and hear that phrase almost daily in the news. Sometimes it’s merely a politician’s or advocate’s opinion, no more reliable than the arrogant “I think I speak for all Americans when I say….” But sometimes the speaker has polling data to back up the claim. For example, a Washington Post/ABC News poll this month found that 57% of adults and 59% of registered voters support a ban on assault weapons, yet that provision was left out of the Senate gun safety bill.

Don’t senators care about popular opinion? Yes, they do, at least on high-profile issues with extensive public debate. But they care about polls in their own states.

“A majority of Americans agree” – with the implication that equals a legislative majority – is an example of the ecological fallacy: the assumption that individuals or subsets within groups share the characteristics of the larger group. Intuition tells us that if 57% of Americans support a ban on assault weapons, then a roughly equal percentage in each state support that ban. But rural voters tend to be far more skeptical of gun safety regulations … and the 25 least populous states contain less than one-sixth of the total population.

That means less than 17% of Americans elect half of the U.S. Senate. Add an inevitable Republican filibuster, and any gun safety bill will need at least 60 votes. Even if you assume each senator will vote with the popular majority in his or her state, that would require 30 states where popular majorities support the assault weapons ban. Given the demographics of gun safety, there may not be even 25.

Yet again, we see an idea that truly is common sense – that a national popular majority should equal a legislative majority – but nonetheless is not true. And that’s a myth we progressives need to accept and plan strategies to overcome, rather than pretending it doesn’t exist.

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Happy Friday!