I have been thinking about common sense for years. I would lump it in with other forms of practical wisdom that function at a middle level of abstraction, along with proverbs, experience (including anecdotal reasoning), and wisdom per se, however we define that. They are an adjunct to philosophical reasoning, which can be too complex and time-consuming to use in dealing with everyday situations. In later essays, I will examine the psychological and epistemological aspects of the these forms of knowing with a particular eye toward oral versus literate thinking. But let's begin with common sense.
I recently took part in a discussion of common sense in the r/philosophy subreddit. It was a great discussion. Almost all the commenters had serious reservations about it. I think I was the only one who was at least mildly in favor of it. Their objections to it can be boiled down to three points:
The concept has no definition.
It is culturally relative and is therefore not objective or universal.
It can be used as a bludgeon to attack people who disagree with you without you giving principled reasons for your positions.
I acknowledge these objections, and they do instill a degree of wariness in me, but I think they can be overcome.
It might be helpful to look at what Ayn Rand said about common sense in the essay "Don't Let It Go"
Americans are the most reality-oriented people on earth. Their outstanding characteristic is the childhood form of reasoning: common sense. It is their only protection. But common sense is not enough where theoretical knowledge is required: it can make simple, concrete-bound connections—it cannot integrate complex issues, or deal with wide abstractions, or forecast the future.
Rand's student Leonard Peikoff had this to add in his lecture series on the philosophy of Objecitivism: "That which today is called “common sense” is the remnant of an Aristotelian influence."
I don't think either of these claims is quite right. Common sense can deal with more than concretes, because it can deal with middle-level abstractions, and it can to some extent forecast the future. And people who are not influenced by Aristotle seem capable of it. I've read about leaders of indigenous tribes who have something that could rightly be called common sense. Still I think their ideas are a good beginning.
I am not sure I can give a formal definition with a clear genus and a single differentia, but I think I can identify some crucial components of common sense, that may together function as a definition.
First, for a person to have common sense they must have a store of "common knowledge" about how the world works. They would have to know, for example, to look both ways before crossing the street and that people can't live on candy.
Second, they must have a reality orientation, at least while they are exercising their common sense. They might have a compartmentalized area of otherworldly faith or dogma, but when they deal with non-philosophical issues, they usually live in the real world. I've seen serious mystics who almost seemed to have split personalities, where one was the mystic and the other had common sense in buckets.
Peikoff would attribute the reality-orientation to the remnants of an Aristotelian influence, but I think that the universal human ability to stay close to perceptual reality (not quite concretes as Rand said, but definitely not very abstract) along with the demands that thriving imposes on us keep most people in the real world much of the time, which isn't to say that they are very good at living in the real world..
Third, they must exercise what I call "critical thinking lite" skills. They must be able to do basic analysis and integration using simple, middle-level principles, including proverbial wisdom. For example, the relevant proverb might be "You can't cheat an honest man," and the common sense application might be a matter-of-fact identification of the fact that the person being cheated engages is wishful thinking i.e. self-deception, i.e. dishonesty with himself. The proverb would channel the observation.
Speaking of proverbs, someone on Reddit pointed out that proverbs can be mutually contradictory, e.g. "Look before you leap," and "He who hesitates is lost." I don't this that this is an issue because proverbs aren't the stuff of philosophy, which has be be systematic and coherent. They are rules of thumb that help the user formulate their thoughts in different contexts.
Part of critical thinking lite is staying calm, reasonably non-reactive, and not letting emotions interfere with one's judgement. There's often an element of shrewdness to the use of common sense.
Can we put these components together to make something like a formal definition? Let's try.
Common sense is an exercise of practical wisdom based on having a store of knowledge about how the world works, engaging reality, and using informal critical thinking skills on a middle level of abstraction.
To return to the three objections:
We do now have a workable definition.
The phenomenon is not culturally relative because we are restricting it to dealing with reality and not culturally relative beliefs such as religious dogmas. I realize we're in danger of the No True Scotsman fallacy here, but I think we can separate the pre-theoretical connection to reality of the common sense person from the often detached-from-reality quality of many philosophical/religious beliefs.
This objection is more difficult to answer, but I would note that claims that one is being logical or rational or even kind can be used as bludgeons against people who disagree as well. There doesn't seem to be any way around this except for introspection (that one is really using common sense) and self-assertion (that one is not going to allow oneself to be steamrolled).
I can understand that some readers might still find the concept of common sense too nebulous for objective use. It might be helpful to work through an example of someone who, I think most people would agree, has little common sense. Let's call him JP.
JP did two years at a good college before dropping out. He clearly thought hustle would get him ahead in the world, so he sold nutritional products door-to-door, among other things. He kicked around for awhile and ended up doing a year at another college. He didn't finish.
Soon he picked up enough skills to make an OK living at a job that was white-collar but beneath his talents. He still had side-projects. He tried to invent variations on products that were already so well-established that he never would have overcome the inertia that they had in the market, but the challenge fascinated him.
Although he had slept with a few women in his life, he mostly likely men, younger, browner men. (JP is white.) He couldn't find anybody here in the States (this is before Grindr, so it might have been difficult to search). So he did some research and lined up 24 men in their early 20s in Southeast Asia as prospects. He established a business partnership (not with one of the 24) and moved there.
Well, of course he got defrauded and lost most of his savings. He ended up living in squalor with one of his boyfriends, while doing online office work for fifty cents an hour. Next he got hit in traffic, resulting in brain damage, which he treated himself with the help of Dr. Internet.
I think you get the idea. JP just had no clue about how to navigate the world. And he couldn't understand why he annoyed some people or why they made fun of him. He just thought that people were being unfair to him for mysterious reasons.
I'll tell one more story to make my point. We lived together for a time after he dropped out of college. Once I did something nice for him, I don't remember what, and he became quite concerned that he needed to something equally nice for me, basically right away. His idea of kindness was strictly quid pro quo. I had to explain that friends don't keep score (although I suppose one has to have some sense of the balance in order not to be taken advantage of).
I've lost track of him, but the last I heard about him was so awful that I do not want to repeat it. I don't think he has given up though.
So there's my example of a lack of common sense. He did hold a vaguely Objectivist worldview when he was in college the first time, which helped him a little, and he didn't have a mean bone in his body, but he almost completely lacked the store of common knowledge that people need to thrive and his critical thinking skills were extremely rationalistic, although he had practical skills like fixing cars.
It's tempting to opine that JP was on the spectrum. Maybe. But he could hold normal conversations beyond his areas of interest. He made eye contact. He didn't have meltdowns, etc. Perhaps he was neuro-atypical in some other way, I don't know. He just seemed to lack common sense. And I think that someone from any other culture who thought and acted the way he did would be said not to have it either.
I believe JP was a good example because you cannot attribute his problems to low intelligence or bad intentions. His lack of common sense, if that really is what was going on with him, seems just to be a character flaw and he could be person out of either a Shakespearean tragedy or comedy, depending on how you want to look at him. I for one don't want to laugh at such a fundamentally decent human being.
To conclude, common sense is a fairly effective way for a non-theoretical person to deal with the world. In fact, since most of philosophy is false and deleterious, common sense might be a better way to operate than theory much of the time. At the very least, a person with common sense can be a breath of fresh air, given their down-to-earth way of living.