 Binkley stipulates that the students do not forget. He needs to add that the students know that they will not forget. For the mere threat of a memory lapse sometimes suffices to undermine knowledge. Consider Professor Anesthesiology’s scheme for surprise tests: “A surprise test will be given either Wednesday or Friday with the help of an amnesia drug. If the test occurs on Wednesday, then the drug will be administered five minutes after Wednesday’s class. The drug will instantly erase memory of the test and the students will fill in the gap by confabulation.” You have just completed Wednesday’s class and so temporarily know that the test will be on Friday. Ten minutes after the class, you lose this knowledge. No drug was administered and there is nothing wrong with your memory. You are correctly remembering that no test was given on Wednesday. However, you do not know your memory is accurate because you also know that if the test was given Wednesday then you would have a pseudo-memory indistinguishable from your present memory. Despite not gaining any new evidence, you change your mind about the test occurring on Wednesday and lose your knowledge that the test is on Friday. (The change of belief is not crucial; you would still lack foreknowledge of the test even if you dogmatically persisted in believing that the test will be on Friday.)