the post hoc fallacy - don't fall for it

I had been worried about my exams. So Jill bought me a rabbit's foot to take with me for luck. I took the foot, and I passed the first exam. So, you see, the rabbit's foot worked! I shall take it to all my other exams, and it will make me pass them, too. This is an example of the post hoc fallacy. Here are two more examples: - John's psychic told him she would send positive psychic vibes when he tried to climb Everest. And he succeeded! so, you see, his psychic really does have miraculous powers! From now on he's always going to ask her for help in climbing mountains. - Local taxes went up. And, look, the crime figures went up. So higher local taxes causes crime. Local taxes should never have been raised! Examine all three examples and you will find that someone concludes that, because one event occured after another, therefore the first event must have caused the second. This is clearly flawed reasoning. Usually, when one event occures after another, there is no casual connection between them. Suppose, for example, that I plug in the kettle. Immediately after, a comet crashes into Jupiter. Did I cause the comet's impact? Obviously not. Of course, there may be casual connections between two events that occur one after the other. Perhaps the rise in taxes really did cause a rise in crime. Perhaps John's psychic really did cause him to succeed. The point is that such 'one-off' observations do not remotely justify the claim that the first event caused the second. The moral is: don't leap to conclusions. Noticing that one event occurs immediately after another might give one grounds for investigating whether two events are casually connected. But it does not, by itself, make it rational to believe that there is any such connection. Unfortunately, superstitious people are very prone to the post hoc fallacy, and the unscrupulous can and do take advantage. Point out that just after someone bought one of your luck rabbit's feet they immediately won some money on a scratch card and you will soon find gullible customers beating a path to your rabbit's foot store.

Its the same people that forward me those &$$^@$^@ chain letters that fall for this.
-frick