The legendary physicist Richard Feynman once said that if you can’t explain something simply, you don’t understand it. The prankster of the Manhattan Project was, alongside being a brilliant scientist, an excellent explainer. The Great Explainer, in fact. The Feynman Lectures on Physics, as they’re known, are famous for both their timeless relevance and their simplicity. He kept a note at the top of his blackboard: “What I cannot create, I do not understand.” Having been thoroughly steeped in the structure of the universe and actively participated in the disassembling of atoms, he knew this stuff inside and out.
Consider if, instead of delivering these boiled-down synopses of complicated aspects of physics, he went a different route. Imagine if he got up in front of a classroom of undergraduates, frowned, and said: “This stuff is all just common sense, really,” and walked out, leaving the students with a Planck-length lecture and a deep inferiority complex.
Common sense as it’s currently understood and commonly used is significantly worse: it is an anti-intellectual memetic weapon deployed to deaden reason and defeat conversation and inquiry. “Common sense isn’t very common anymore,” is something I once smugly thought to myself. Like everyone else who uses the term in this way, I was being pretentious and working to narrow the bounds of my own understanding, not expand them.
In modern parlance, common sense is more of a social signal than an appeal to reason. It says: “This is something you’re supposed to believe.” But many things that appear to be common sense are far from it. Take the fact that the Earth is round. Indisputably true? Of course. Common sense? Hardly. Do you know how the Ancient Greeks came to that conclusion? They spotted the shadow of the Earth on the Moon during an eclipse. That’s not common sense, at all; that’s an uncommon level of attention and deductive power at work.
So what is common sense? In one sense, it is a real thing: a relatively universal ability to reason and come to practical conclusions. Humans are on average very similar, and it’s not at all unreasonable that, equipped with similar hardware and software, we might come to common conclusions. Across cultures and ethnicities we have the same ability to reason.
This is the sense in which Thomas Paine used the term for his legendary pamphlet. But anyone who has read Common Sense has sat down for the procedure. Had Thomas Paine used the term in its modern understanding you could’ve read it in the time it took you to sit down. “Monarchies are bad. Britain is bad. It’s just common sense.” Fin.
But Paine’s pamphlet is packed with not only assertions but proofs. Thomas Paine meant only that his work could reasonably be understood by anyone, and that anyone could reason along with him.He laid out his argument clearly, in plain language, such that anyone who could read could consider his claim, and he wagered you would agree because you shared the same sense he had.
How often have you heard common sense used that way in your life? I’m going to guess precisely never.
It probably sounded more like this: either it was uttered in a frustrated tone after a protracted conversation or stated flatly and curtly at the very outset. In the latter case, it was hard to resurrect the conversation. In the former, the tone made it clear that pressing the issue was going to piss someone off. Either way, it meant the conversation was dead.
But stating something is common sense is, frankly, useless by way of explanation. If your claim is confirmed by common sense, that means there’s a very simple reason that it’s true. Saying it’s common sense accomplishes nothing except to tell the person there’s a very simple explanation. The reasonable thing is to just say it. Invoking common sense is just wasting time. It’s that moment in an action comedy after a bystander has stumbled into the scene, gawking at the upside down flaming police car sticking out of the fourth floor of an office building as the protagonist, wearing a clown suit and holding a stick of dynamite and an inflatable dolphin says: “It’s not what it looks like.”
So why do people say it at all?
The fact that people persist in an apparently useless behaviour tells us that the behaviour is working. We’ve just misunderstood the purpose of the behaviour.
Consider the consequence. Common sense, in practice, is a conversational dead end. Invoking it shuts down the conversation. That tells us that that’s the goal. It isn’t to enlighten or clarify. It’s meant to get you to stop talking.
The practical implications of this are similarly two-fold. First and foremost, don’t be bothered whatsoever if someone invokes common sense against you in conversation. It is designed to shut down the conversation and antagonize reasoning and is generally deployed by someone whose beliefs are under threat. If you feel ashamed or embarrassed when someone dismissively tells you “it’s just common sense,” understand you were meant to feel that way. By making you feel that way, they’re punishing you for pressing the issue and threatening their beliefs. Recognize that if you’re discussing something with someone in good faith and they bust out common sense and can’t follow it up, they’re no longer interested in a good-faith discussion. Take that for whatever it’s worth. Sometimes people have confused themselves into thinking their intuition is their reason. Sometimes they just need a break. Sometimes they aren’t interested in having a particular belief challenged. Whatever the reason, when you hear “common sense,” translate it as “I don’t want to talk about this anymore.”
The second use of this understanding applies to yourself. Just as we can be threatened by others examining our beliefs, so too can we use the mantra of common sense as a shield against self-examination.
Consider your own common-sense beliefs, and listen when you find yourself unexpectedly invoking it, whether during discussion or rumination. If it’s common sense, it should be very simple to explain and break down. If you’re thinking it through and having a hard time, persist. You’re likely on to something.
What we think of as common sense is often an inheritance: Things our parents, respected peers and the educated believed — but didn’t want challenged — were passed to us under the label. The function of common sense in that case was to ease the exchange. Common sense is in this sense focused on the common aspect: getting community members to absorb community beliefs with minimal fuss. But this is one of the ways dead truths persist. If you dig down on a belief you consider and you realize the only reason you believe it is because someone told you it was the case, understand that you don’t actually understand it.
This isn’t the end of the world. Most of us are going to have beliefs that we don’t fully understand. That’s life. There isn’t sufficient time or energy to ground-truth everything. As Carl Sagan once said, “If you wish to make an apple pie from scratch, you must first invent the universe.” Nobody has time for that.
There are things that you can do to resurrect dead truths (examining the veracity of your sources is faster than trying to build the whole concept from the ground up, for example), and there are definitely beliefs of yours that you will want to build from the ground up, or at least give more than a cursory examination. But you can’t do that if the common-sense roadblock is in your way.
I don’t just mean this in the sense of challenging your own beliefs, but also of bringing them to life. Just because you arrived at a belief by way of intuition or cultural osmosis doesn’t mean it’s wrong. Just understand that common sense is not a way of confirming the correctness of an idea. It’s a weapon wielded against criticism, designed to defeat a rational challenge by inducing an unpleasant emotion to punish the challenger. It’s bad enough if someone brings it to bear against you, but if you wield it against yourself, your ability to advance your knowledge and understanding is severely truncated. At a societal level, it can be used as a way of allowing necessary myths to persist. On a purely rational basis, these ideas can be questionable, if not absurd. But if they’re functional for that society and inquiry is punished, they can survive much longer than they have any right to.
In Portions from a Wine-stained Notebook, fiction writer Charles Bukowski said that: “Genius could be the ability to say a profound thing in a simple way, or even to say a simple thing in a simpler way.” In that respect, Feynman was certainly a genius. In that respect, many of us would like to believe we are geniuses. The invocation of common sense is an easy shortcut, but it obscures the path to actual understanding.