A Cautionary Tale. As a Southerner living in Virginia in the 18th century, Thomas Jefferson once encountered a jaw-dropping claim, and it came from two eyewitnesses. They said they had seen rocks fall from the sky. Rocks from the sky. They even claimed to have retrieved fragments from them. And the witnesses, under normal circumstances, would be considered pretty darn good ones: two Harvard professors living in New England.
But Jefferson didn’t believe them. Why? Because Southerners don’t like Northerners? No. It was for lack of coherence. Insofar as Jefferson knew, rocks don’t fall from the sky, and so, in his estimation, the witnesses were either lying or simply mistaken.
Concerning the incident, he wrote the following: “I could more easily believe that two Yankee professors would lie than that stones would fall down from heaven.”
Jefferson, in other words, possessed a Weltanschauung—a worldview, a paradigm, a model for the way the world is and works—that could not accommodate such a claim at face value. What Jefferson thought he already knew simply did not match what the witnesses said. He saw no way to make the claim and his background knowledge cohere, and so he dismissed the claim. “Stones do not fall down from heaven.” It was logically possible—one could imagine such an absurd event—but he took it to be scientifically impossible, physically impossible.
And, of course, he was wrong. We now know that rocks can and do sometimes fall from the sky—as meteors. But how did a smart fellow like Jefferson reach a conclusion that now strikes us as ludicrous?
In this instance, his error was that he did not bring sufficient critical reflection upon both the new claim and his existing Weltanschauung. His skepticism went in just one way, toward the new claim and away from his worldview. And we can certainly forgive Jefferson, for we readily do the same thing. If someone was to tell us that she saw a penguin fly overhead, we might readily draw the conclusion that she’s a lunatic or on drugs, for we know that penguins can’t fly. We know it. It’s part of our background knowledge. The claim must be false. There must be another explanation.
So it was good that Jefferson sought coherence between the Harvard professors’ claim and his background knowledge. What we think we already know about the world should match any new claims made about it. But Jefferson failed to reevaluate what he took for knowledge, and this in spite of the fact that he had a good reason to do so (emphatic testimony from two reliable sources claiming to be in possession of evidence). So he was a bit flippant and careless.
The lesson here: check your premises. What do you think you know and how do you know it? What do you think you should do and why do you think you should do it? Do you really have good reasons and evidence for treating your premises as sound? How did you acquire them in the first place? As a wag once said, “Too quickly assuming things makes an ass of you and me.”