F.D. Flam

If you hear a politician or salesperson or, for that matter, opinion columnist invoke common sense, beware. When people say a particular view on immigration, foreign policy, abortion, or climate is just “common sense,” they are implying that those who disagree have no common sense — and therefore must be idiots.

It’s a widespread rhetorical tactic. Former President Donald Trump often appeals to common sense — whether on immigration or Jan. 6. President Joe Biden has asked for “common-sense gun control.” The Union of Concerned Scientists used the phrase in an argument about climate change. I even used it in a column about COVID mask policies.

When scientists recently probed the idea of common sense using thousands of volunteers, the only beliefs people shared were concrete observations of the world — that gravity makes things fall, that triangles have three sides — not the kinds of things that require debate and persuasion. The results were published in the Proceedings of the National Academy of Sciences.

The researchers, from the University of Pennsylvania, tested more than 4,000 statements that were termed common sense in media references or political campaigns. They also tested widespread aphorisms, including some by Benjamin Franklin. And they asked their volunteers to offer their own common-sense statements. A few examples: “Perception is the only source of knowledge,” “Rudeness is the weak man’s imitation of strength,” “Numbers don’t lie,” “All human beings are created equal,” and “Avoid close contact with people who are ill.”

The researchers wanted to know which statements not only got wide agreement but were perceived as uncontroversial — people assumed they would be agreed upon by most others. The result: There was very little sense that was truly common.

This should help us all think more critically when the phrase gets bandied about in political rhetoric — or anywhere. “It’s not just in politics but also in everyday life,” said computational social scientist Duncan Watts, who co-authored the study. Earlier this year he was serving his jury duty, he said, “and it was really interesting how frequently, in her instructions, the judge told us to rely on our common sense.” 

What people think is common sense is idiosyncratic. When politicians or salespeople refer to it they may be trying to flatter their followers and insult their opponents.

Looking back to the column in which I used that phrase, I wrote that common sense would dictate that if the risk of disease transmission in some settings is negligible, masks should be optional. A better argument would have relied on logic and evidence: Outdoor masking has negligible benefit in preventing viral transmission and outdoor masks make it harder for people to get the mental and physical health benefits of going outside, ergo, outdoor masking should be optional.

Watts was inspired by a 2014 book, “Common Sense: a Political History by Sophia Rosenfeld.” In it, he said, she tracks how common sense became associated with good — something people wished to possess or feared they lacked. (Famously, “Common Sense” was the title of the influential Revolutionary War pamphlet by Thomas Paine, but the tract never mentions common sense after the title.)

What’s perceived as common sense varies by time, place, and culture. In the 1700s, a Scottish professor named James Beattie listed a number of things he considered common sense: Things equal to one and the same thing are equal to one another; Ingratitude ought to be blamed and punished; I have a soul distinct from my body; Virtue and vice are different; Truth exists; and There is a God. 

Watts says he thinks common sense is part of a larger issue he calls uninterrogated knowledge — things people think they know but haven’t examined with a critical eye. People think they know what they mean by truth, misinformation and fairness, but these concepts are fuzzy and subjective.

It would be nice if common sense existed. Then, all we’d have to do was turn it on and we’d suddenly come to agreement on divisive political matters, difficult legal deliberations, and bitter personal disagreements.

As for my falling back on common sense in a column, I can now see how that tactic forecloses a useful discussion. There’s a productive, illuminating debate to be had between disagreeing sides — and it won’t be solved by appeals to common sense.

F.D. Flam is a Bloomberg Opinion columnist covering science. She is host of the “Follow the Science” podcast.