In his new book Elastic: Flexible Thinking in a Time of Change, the renowned American popular-science writer Leonard Mlodinow tells a story that is both hilarious and exasperating—
A defendant went on trial after being accused of murdering his wife. The circumstantial evidence was very much against him, but the prosecutor lacked a piece of direct evidence that could clinch the case—because the police had never managed to find the defendant’s wife’s body. So, in his closing argument, the defense lawyer kept trying to make the jurors realize that they actually had no evidence “beyond a reasonable doubt” that the defendant had killed his wife.
“Beyond a reasonable doubt” is a key principle in American criminal trials: if you want to convict a defendant, you need evidence “beyond a reasonable doubt.” Evidence that merely creates “reasonable doubt” isn’t enough.
For example, suppose you find a body in my living room. There’s a knife beside it, my fingerprints are on the knife, and the defendant’s blood is on me—evidence like that could create “reasonable doubt” and make you suspect I’m the murderer. But in an American court, it still couldn’t convict me, because you couldn’t rule out other explanations. Maybe someone killed the person in my living room, and I only touched the knife and got blood on me while trying to save them. Only when CSI examined the crime scene and proved that the blood on me could have been distributed that way only if I had been holding the knife and stabbing someone at close range would it barely qualify as evidence “beyond a reasonable doubt”—because it would make the explanation in my defense extremely hard to sustain.
So, evidence “beyond a reasonable doubt” is evidence that almost completely rules out every possibility other than the murderer having committed the killing.
Back to the case from earlier. Since the wife’s body had never been found, the claim that “the murderer’s wife is dead” hadn’t even met the standard of “beyond a reasonable doubt,” let alone the claim that “the defendant killed her.”
That’s how it works in theory—but how do you get a jury to understand the point?
Seeing that reason alone wasn’t going to persuade the jury, the defense lawyer had a sudden inspiration. He turned to the jury and said: Actually, we’ve found the alleged victim in this case. She’s in the courthouse right now, and in a moment she’ll walk through that door behind you, proving that my client is innocent.
The moment he said this, every juror turned around to look at the door. A few seconds passed. Naturally, no one came in.
The lawyer then announced triumphantly: Unfortunately, we haven’t actually found the victim. But didn’t every one of you just turn around in eager anticipation? Doesn’t that prove that, deep down, you completely believe there’s a possibility the victim is still alive? If her death had already been established beyond a reasonable doubt, none of you would have turned around just now.
—Up to this point, it was an absolutely brilliant move. When you’re persuading people, appealing to emotion works better than appealing to reason. But what works even better than appealing to emotion is getting the other person to put your point into practice through their own actions. And this lawyer actually managed to do that.
So, was the jury persuaded?
Almost.
Because the prosecutor had noticed something crucial: there was only one person in the entire courtroom who hadn’t turned around to look at the door—the defendant!
The one person who can’t be deceived by a lie is the person who knows the truth.
Precisely because the defendant was the murderer, he alone knew that his wife would absolutely not walk through that door again.
The lawyer’s brilliant move had “unfortunately” dragged his own teammate into the pit too.
The defendant’s reaction, ironically, constituted evidence “beyond a reasonable doubt.” In the end, the jury found him guilty of murder.
p.s.:
Elastic: Flexible Thinking in a Time of Change is a somewhat hard-to-review book. It contains plenty of entertaining studies and anecdotes, but many of those passages feel as if the author got carried away while writing, went a little high, and dropped them into the book. They don’t quite connect with the logic of the book as a whole. They’d be hard to organize in Psychology New Knowledge Course, but distilled into a short article here, they work exceptionally well ^_^
Note
- The articles in this “Psychology New Knowledge Mini-Course” series were short popular-science miscellanies written to accompany the content of Zhichao Wei: Psychology New Knowledge Course at the time, and were published on the now-closed platform Fantuan. The original article link no longer exists.
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