  We may illustrate this by asking: When the dunce who supposes that 5 + 7 = 11 decides to activate some item of knowledge to be the answer to “What is the sum of 5 and 7?,” which item of knowledge does he thus decide to activate? At first only two answers seem possible: either he decides to activate 12, or he decides to activate 11. If he decides to activate 12, then we cannot explain the fact that what he actually does is activate 11, except by saying that he mistakes the item of knowledge which is 11 for the item of knowledge which is 12. But this mistake is the very mistake ruled out as impossible right at the beginning of the inquiry into false belief (188a–c).  Alternatively, if he decides to activate 11, then we have to ask why he decides to do this. The most plausible answer to that question is: “Because he believes falsely that 5 + 7 = 11.” But as noted above, if he has already formed this false belief, within the account that is supposed to explain false belief, then a regress looms.