unexpected examination paradox a paradox about belief and prediction. One version is as follows: It seems that a teacher could both make, and act on, the following announcement to his class: ‘Sometime during the next week I will set you an examination, but at breakfast time on the day it will occur, you will have no good reason to expect that it will occur on that day.’ If he announces this on Friday, could he not do what he said he would by, say, setting the examination on the following Wednesday? The paradox is that there is an argument purporting to show that there could not be an unexpected examination of this kind. For let us suppose that the teacher will carry out his threat, in both its parts; i.e., he will set an examination, and it will be unexpected. Then he cannot set the examination on Friday (assuming this to be the last possible day of the week). For, by the time Friday breakfast arrives, and we know that all the previous days have been examination-free, we would have every reason to expect the examination to occur on Friday. So leaving the examination until Friday is inconsistent with setting an unexpected examination. For similar reasons, the examination cannot be held on Thursday. Given our previous conclusion that it cannot be delayed until Friday, we would know, when Thursday morning came, and the previous days had been examination-free, that it would have to be held on Thursday. So if it were held on Thursday it would not be unexpected. So it cannot be held on Thursday. Similar reasoning supposedly shows that there is no day of the week on which it can be held, and so supposedly shows that the supposition that the teacher can carry out his threat must be rejected. This is paradoxical, for it seems plain that the teacher can carry out his threat. See also PARADOX. R.M.S.