In a recent article entitled “Scepticism and Knowing That One Knows” (Canadian Journal of Philosophy 6, pp. 655–63), Michael Hall poses a sceptical argument based upon two rules of inference:

where ‘Kp’ stands for ‘it is known that p'. The argument goes:

Hall (rightly, in my opinion) attacks R2, but he says little about R1. I wish to add a few words of warning about R1 as well.