An advertisement on a billboard displays the message to passing motorists, "honk if you don't use Blind-O Window Cleaner." Based on this advertisement, which of the following statements can be concluded? a) A driver who reads the sign and then honks in response to it must not use Blind-O Window Cleaner. b) A driver who does not use Blind-O Window Cleaner will honk after reading the sign. c) Based on this advertisement, it is possible to determine a motorist's use of blind-O window Cleaner if that motorist does not honk after reading the sign. d) If a driver uses Blind-O window cleaner, he or she will not honk after reading the sign. e) A driver who reads the sign and then does not honk must not use Blind-O Window Cleaner

来源eterson's Logic Review

正确答案是 e).

书上解释如下:

The premise of this argument is presented as an if-then syllogism. The trick is that the sentence is inverted. It is easier to understand if you invert sentence to read, if you don't use Blind O Window, than honk? With an if-then argument, a valid conclusion may be reached if you are told that the if clause is false. Therefore, knowing that a driver does not use Blind O window cleaner can result in conclusion that the driver will NOT honk. Conversely, knowing that the driver is not honking can result in a conclusion that the driver does use Blind O window. Hearing a driver honk is not sufficient to draw any conclusion, since that driver could be honking merely in relation to the traffic or for some other reason. Therefore, answer A is incorrect.

还是不明白,请高人赐教