Anyone who gets to know my opinions on common sense will quickly discover that I loathe the phrase and quickly dismiss the opinion of anyone using it as wrong. I’ve never really explained it though, it’s normally not worth the effort, but I decided to write it down.

I think saying “it’s common sense” shows a complete failure to use your theory of mind and is almost inexcusable.

The theory of mind¹ is something every one of us develops as a child. This is a theory in the scientific sense - an explanation for observed behaviour when we cannot access the actual system being explained. It’s the realisation that other humans have their own set of knowledge, experience, and emotions, and the ability to judge another’s behaviour in the context of their separate mind.

We know everybody experiences life differently, and that somebody else would react in a completely different manner than you would in any given situation. Unfortunately the use of our theory of mind peaks in childhood and a lot of adults completely ignore it because things don’t suit their world view.

This is the crux of why I hate the phrase “common sense”: it means “I would have done this and cannot imagine any reason why someone would do something different, so it must be a moral failing” but we already know that everyone reacts differently and why.

To pick a few examples, I grew up in farming areas so if I see a field with cows and calves in my path I will attempt to find a different way, or if I can’t make sure I keep a large distance between myself and any of the animals. Why? I know three things - all animals are protective of their young, humans look like predators, and as a prey animal cows do not make any threat display prior to attacking. You won’t know a cow is coming for you. People who grew up in cities have no reason to know this, cows do not play any role in day to day life.

Similarly when cooking I crack eggs individually in to a small bowl to check if they’re still good, because chickens don’t stamp a best before date on them. Yes I could float test, but that’s another task. If you’ve always bought eggs from the store you’ve never needed to worry.

And finally I know that I shouldn’t try to skip the airport security line because airport security is serious.

So that’s why I hate “common sense” - it’s just shorthand for an egocentric lack of understanding that people don’t all have the same knowledge. If there’s a problem the solution is aways education and not assumption.