Matters which are predominately conceptual leave room for doubt, they retain a hypothetical quality even if they are well-confirmed. The possibility of their being otherwise is part of the territory, part of what enables them to have the credibility that they currently possess. What vcertainty there is is other-validated. That the whole world might be a dream is part of what makes this the kind of world that it is. It is not to be resisted but merely observed that a gap remains open in even the most compelling constructions. Hidden premises have already been discovered and no limit can be set on there not being yet deeper hidden premises, exceding your ability to currently imagine. What certainty is, in this kind of world, is a comportment towards the fringe of doubt, the trace of negativity like a grain of salt needed to develop the entire picture. This is concomitant with the positivity of the self, even if you can never include the self within the picture. If there is an inverse experience, a no-self experience to express it oxymoronically, it is that instead of what is known as doubt being at the fringe of consciousness it is at its centre and is wide open. Then it can no longer be called doubt, it appears to be that very impossibility of a self-validating certainty. This is the name you are tempted to give it by contrast with your previous epistemology, although it makes no sense in this context. It is a complete surprise and shows you that you are no longer experiencing via concepts.