The topic of common sense recently came up in the comment section of this blog, and after initially responding with a comment I thought it would be worthwhile to expand on my comment and explain why "Common Sense" is a misnomer.
Let's start with the comment that set me off. Felix Torres left a comment explaining that:
It used to refer to a minimum level of rationality that could be expected from an adult, based on things that are common knowledge: things like not going surfing in hurricane weather or sticking a finger in a light bulb socket.
Darwin awards prove how uncommon it has become.
My problem with his explanation is one, the assumption that common sense is any less common today than it was a hundred years ago, and two, the assumption that anything described as common sense is true or correct.
I'll address those in reverse order.
Many people share the assumption that a common sense saying must be correct, but based on how I have heard the term used that simply isn't the case. Here's my understanding of the meaning and use of common sense.
In my experience common sense is and always has been a synonym for "the assumption of shared culture or knowledge". Or as the apocryphal Albert Einstein saying goes, "Common sense is the collection of prejudices acquired by age eighteen."
When the term common sense is used, it says nothing about the topic at hand and instead merely indicates that the speaker is assuming something to be both true and common knowledge.
What is assumed to be true can range from factual info (such as math or geography) to best practices, urban legends, or possibly racist/sexist/bigoted assumptions like "it's common sense that all blacks/women/gays/ethnic group are (blank)".
I came to this revelation when a forum I used to help run was discussing whether to ban shortened URLs. One person said that it was common sense that you can't trust the shortened URLs, which is simply nonsense. They're used all over, and the only time they're not safe is when used by a malicious actor.
That person had simply assumed it to be true, when in fact he had apparently never confirmed his assumption. This is why I immediately question any argument that ends with "it's common sense".
In my opinion, "common sense" should be regarded as a logical fallacy, perhaps as a thought terminating cliche (a clichéd phrase in and of itself may be valid in certain contexts, its application as a means of dismissing dissent or justifying fallacious logic is what makes it thought-terminating).
That is how I see it used most often, and it is frequently followed by the lamentation that common sense simply isn't as common as it used to be.
Speaking of which, it might surprise you to learn that regretting the decline of common sense is not a recent phenomenon; it's a meme which dates back a couple centuries. Will Rogers is credited with saying almost a hundred years ago that "Common sense ain't common", and half a century before that Horace Greely quipped "Common sense is uncommon."
So not only is common sense not common today, it never was. The only part of common sense which is actually common is the way its absence is noted, so much so that it almost exists in a negative space.
P.S. There's about another 400 words cut from this post which expand on the timelessness of common sense as a meme, but I pulled it because I found the quotes I was going to use are as fake as the belief that common sense used to be more common in the past than it is today.
P.P.S. Do you know those quotes by ancient Greek philosophers lamenting about "kids these days"? They are most likely apocryphal.
image by cogdogblog