One day a man met Socrates and said, “Do you know what I just heard about your friend?” “1 a minute," Socrates replied. "Before you talk to me about 2 friend, it might be a good idea to take a moment to filter (过滤) what you're going to 3. I call it Three Filter Test. The first filter is Truth. Have you made absolutely 4 that what you are about to tell me is true?" "Well, no," the man said. “5 I just heard about it and ..." "All right," said Socrates.  "So you don't really know if it's true or not. Now, let's try the second filter, the filter of 6. Is what you are about to tell me about my friend 7 good?" "No, on the contrary..." "So," Socrates continued, "you want to tell me something bad about my friend, but you're not certain it's true. You may 8 pass the test though, because there's one filter left - the filter of Usefulness. Is what you want to tell me about my friend going to be 9 to me?" "No, not really." "Well," concluded Socrates, "if what you want to tell me is 10 true, nor good, nor even useful, why tell it to me at all?"