A Roman came to Rabbi Gimzo the Water Carrier, and asked, "What is this study of the law that you Jews engage in?" and Gimzo replied, "I shall explain. There were two men on a roof, and they climbed down the chimney. One's face became sooty. The other's not. Which one washed his face?" The Roman said, "That's easy, the sooty one, of course." Gimzo said, "No. The man without the soot looked at his friend, saw that the man's face was dirty, assumed that his was too, and washed it." Cried the Roman, "Ah ha! So that's the study of law. Sound reasoning." But Gimzo said, "You foolish man, you don't understand. Let me explain again. Two men on a roof. They climb down a chimney. One's face is sooty, the other's not. Which one washes?" The Roman said, "As you just explained, the man without the soot." Gimzo cried,"No, you foolish one! There was a mirror on the wall and the man with the dirty face saw how sooty it was and washed it." The Roman said, "Ah ha! So that's the study of law! Conforming to the logical." But Rabbi Gimzo said, "No, you foolish one. Two men climbed down the chimney. One's face became sooty? The other's not? That's impossible. You're wasting my time with such a proposition." And the Roman said, "So that's the law! Common sense." And Gimzo said, "You foolish man! Of course it was possible. When the first man climbed down the chimney he brushed the soot away. So the man who followed found none to mar him." And the Roman cried, "That's brilliant, Rabbi Gimzo. Law is getting at the basic facts." And for the last time Gimzo said, "No, you foolish man. Who could brush all the soot from a chimney? Who could ever understand all the facts?" Humbly the Roman asked, "Then what is the law?" And Gimzo said quietly, "It's doing the best we can to ascertain God's intention, for there were indeed two men on a roof, and they did climb down the same chimney. The first man emerged completely clean while it was the second who was covered with soot, and neither man washed his face, because you forgot to ask me whether there was any water in the basin. There was none.