Once upon a time, you and I might have had a conversation like this:

     You: “Well, obviously, the world is flat.”

     Me: “Of course it is. Just look around you!”

     You: “I mean, it’s just common sense!”

To us, this conversation would have sounded rational, with your use of ‘common sense’ seeming entirely appropriate. Nowadays, it just looks silly.

I was once interviewing dieticians for a qualitative research study on children’s health. When a participant said, “a good breakfast is essential to a child’s health,” I asked her how she knew that. After some back-and-forth, during which she was unable to cite evidence, she snapped, “for God’s sake, it’s common sense! Everybody knows this!”

And that’s the problem with ‘common sense.’ It’s a term that can make something seem rational and correct, even when it might be neither.

I once wrote a post on being skeptical of intuition, and those principles apply here. Common sense can be useful, but can also lead you astray. Here’s why you should be skeptical of common sense, whether it’s your own or somebody else’s.

The term has a broad range of meanings:

Practical wisdom. Knowledge of how the world works gained through everyday experiences, leading to better problem-solving and decision-making. In other words, street-smarts.

Intuitive understanding. A grasp of basic truths without the need for topic-specific knowledge or education.

Sound judgement. An ability to assess situations based on critical thinking and sensible reasoning.

Cultural norms. Shared values and beliefs within a specific society, creating unwritten rules and expectations governing behavior.

And, its meaning can be difficult to pin down because:

It’s heavily influenced by culture. Members of an ethnic or religious community might see certain moral principles as common sense, while outsiders might consider them bizarre.

It’s subjective. My common sense could be your nonsense. Common sense is informed by pre-existing biases and assumptions. Also, if you hear something frequently enough, it could start to make sense, no matter how crazy it might be.

It’s less reliable in complex or highly technical situations. If you’re fixing a screen door, common sense can help, particularly if you’ve done it before. But, in the control room of a nuclear plant, common sense alone isn’t going to be enough.

This is not to say that common sense is of no value. It can be reliable, particularly with familiar and straightforward matters. However, in complicated and unfamiliar situations, common sense could lead to errors or misconceptions. Common sense might tell you that you’re healthy, as you look and feel okay. But lab results might say otherwise.

Common sense can be where your assessment of a situation begins, but probably shouldn’t be where it ends. It’s important to seek reliable evidence to support our conclusions. Ultimately facts – not gut feeling – must carry the day.