The demand for common sense is a favorite tactic of debaters who have no facts or logic to support their claims. It’s the lazy choice to say that the proposition being pushed is true because it’s true or is true because a lot of people believe it — in other words, the fallacies of begging the question or bandwagon appeal.
The term, common sense, like so many other words and phrases in a living language, has gone through significant changes since its first recorded usage in the fourteenth century in English. Originally, it meant one of the five wits, the five internal senses, that all human beings are supposed to have. As time went on, the meaning shifted more to a synonym of “good sense,” being reasonable. This is essentially the way it’s being used these days — if you have good sense, you’re supposed to agree with the person making the failed argument. But there was one further development, exhibited by Thomas Paine in his book whose title uses the phrase in question. By “common sense,” he meant what another Thomas, Jefferson, had in mind when he called some things “self-evident.”
In that sense, the thing being identified cannot be denied without descending to absurdity. To claim the contrary is logically impossible. The law of non-contradiction is one example of this. A thing cannot simultaneously exist and not exist. A woman cannot be simultaneously pregnant and not pregnant. And so forth.
But so many things that are today called common sense are by no means self-evident. And to use Hitchens’s razor — whatever is asserted without evidence can be dismissed without evidence — when someone says that a thing is just obviously true and refuses to offer any facts and logic in support, that’s a prime candidate for being challenged.
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