A man walks into a bar, takes a seat on the next-to-last stool, and spends the evening chatting up the empty stool next to him, being charming and flirtatious, as if there were a beautiful women in that empty seat. The next night, same story. And the next night, same story again. Finally the bartender can't take it any more. She asks, "Why do you keep talking to that empty stool as if there were a beautiful woman in it?".
The man answers, "I am a philosopher. Hume taught us that it's logically possible that a beautiful woman will suddenly materialize on that stool, and no one has ever refuted him. If one does appear, then obviously I'll seem very clever indeed, and I'll have the inside track with her."
"That's ridiculous", says the bartender, who happens to be a physicist. "Plenty of very attractive women come to this bar all the time. You're reasonably presentable, and extremely articulate; if you applied your charm on one of them, you might succeed".
"I thought about trying that," he replies, "but I couldn't prove it would work.