Tired of just scraping by? Put propositional logic to work for you! Use these simple steps to convince your friends that they have no choice but to hand over large sums of cash.

WARNING: People may react unpredictably to being tricked out of $10,000. The author assumes no responsibility for any mayhem that ensues when you try this at home. Con responsibly.

Step 1: Gather the Materials

You will need:

Step 2: Choose Your Mark

Put some thought into choosing the right person to approach. You want someone who will take the loss in stride, but still be willing to make good on the bet. Someone with a good sense of humor is key. If they are wealthy enough that $10,000 is no big deal, so much the better, but any avid gambler will do. It is especially helpful to find someone who likes to be right and who will go to great lengths trying to outsmart you.

Step 3: Seed the Pot

Tell your friend you'd like to make a deal to test his propositional logic skills. Hand him two $10 bills. Tell him he can win some or all of the money if he agrees to something first. Say: "I'm about to make a statement. If you want the deal I'm proposing, you have to promise to give me back one of the bills if the statement is false. But if the statement is true, then you can keep both bills."

If he hesitates, add "That's a pretty good deal, isn't it? You are bound to get at least $10, and possibly $20!"

Step 4: Make Your Move

When your friend agrees, make this statement:

"You will either give me one of those bills or you will give me $1,000."

If this statement is false, he will have to give you one of the $10 bills per the agreement you made beforehand. But that would make the statement true, which would be a contradiction. So the statement can't be false, it must be true.

So it is true that he either gives you one of the bills or he gives you $1,000, but he can't give you one of the bills because the agreement was that if the statement were true he is to keep both bills! Therefore he will have to give you $1,000.

Step 5: Up the Ante

Your friend will be understandably upset, so it is only polite for you to give him a chance to save face. Let him know that you're feeling generous, so you will give him a chance to win back the $1,000 on the condition that he answers a yes or no question truthfully.

When he agrees, ask this question:

"Will you either answer NO to this question or pay me $10,000?"

This is a question about whether one of these two options holds:

  1. He will answer NO
  2. He will pay you $10,000

If he answers "no" he is claiming that neither alternative holds, but #1 did hold so "no" cannot be a truthful answer. Hence he must answer "yes" and pay you $10,000.

Step 6: Play the Odds

At this point your friend will be really down, and you'll want to make amends. Tell him you are very sorry that he now owes you $10,000, but being a kind person you're willing to give him a 50/50 chance to win it back again.

Write something on a blank slip of paper, fold it up, and hand it to an onlooker. Explain to him that you've written a description of an event which might or might not take place in the room sometime in the next fifteen minutes. His job is to predict whether or not the event will take place.

Hand him another slip of paper and the pen. Tell him that if he predicts the event will take place, write "yes." Otherwise, write "no." When he writes something down, ask "Have you made your prediction?" Then say: "I'm sorry, my friend, but you lose!"

Open up your slip of paper to reveal the message: "You will answer NO." If he wrote "yes," he is affirming that the event will take place, which it didn't. If he writes "no," he is denying that the event will take place, which it did.

Either way, he loses, and the $10,000 is yours to keep, fair and square.

Best to leave while he is still feeling bewildered.

Step 7: Credit Where Credit Is Due

This Instructable is adapted from Raymond Smullyan's work The Godelian Puzzle Book, which contains many other ideas for using coercive logic to win stuff from your friends and infuriate people. It also gives a more thorough explanation of the ins and outs of the mathematical reasoning behind the cons presented here. Check it out!

Aside from the book cover, all of the images for this Instructable are from flickr, and are licensed for reuse under various Creative Commons licenses. They are, in order of appearance:

<p>If I was the target, I'd just kindly smirk, stay silent and attempt to walk away with the $20. If the con man protests, I'd toss the money on the ground and keep walking. We'd never even make it to round 2.</p><p>That is an option here, right? :)</p>
Just get an honest job like honest folk!
<p>Let's see;</p><p>Try step four on me, I give you one bill and keep the other.</p><p>Step five, and I just say &quot;yes&quot; - you have no indication to which part of the statement I am saying yes (I might be saying &quot;yes, I will say no&quot;), therefore the statement is true and I get to keep both bills.</p><p>Step six, I say &quot;yes&quot;, and still have fourteen minutes and thirty seconds to say the word &quot;no&quot;. Another $20 you owe me.</p><p>Lesson in life - trying to con cash out of somebody with a knowledge of logic or an interest in semantics will cost you $50...</p>

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