The truth behind currency

Jack: Did cavemen have money?

me: No I think they traded stuff.

Jack: Like rocks?

me: I guess. One caveman might have had a pretty rock and traded it for some corn.

Jack: Like loose corn, from a can?

me: They didn’t have cans. Remember? They probably grew corn so the guy probably traded one ear of corn for a rock. I’m guessing here.

Jack: Is that worth it?

me: I don’t know. I guess. If you’re hungry. A rock isn’t worth much, but you can eat corn.

Jack: Then how come I owe you $4.99 from my piggy bank for my new Miles Axlerod car?

me: Because I bought it for you after you said you wanted to use your piggy bank money.

Jack: But I didn’t use my money.

me: Sigh. I know. I bought the car for you, so you owe ME the money.

Jack: How is that possible!? You paid with a CREDIT CARD! So I should get to keep that. Gimme it back!

me: I have to pay the credit card company, so you owe me the money. What if I told you to spend your own money to get the car, and we drove back home and got it out of your bank. Would there still be $4.99 in your bank after you bought the car?

Jack: No, I would have spent it on the car.

me: Exactly. Now you have the car, so shouldn’t your bank be empty?

Jack: But you bought it for me!

me: No, I helped you buy it because you didn’t have your money. It’s only fair that you pay me back.

Jack: (gives me a look) What if the caveman just hit the other guy in the head with the rock and took the corn? Then he’d have the rock AND the corn.

me: (Wait, am I being threatened here??)