Objective Certainty
Objective certainty is not tied exclusively to conclusive reasons or self-evidence. It may be grounded in the absence of intelligible doubts .... Grounds for doubt are not as easy to come by as skeptics think. Fairy-tale imaginings (e.g. brains-in-vats) don't count. --Michael Williams, Lecture, "Wittgenstein on Knowledge & Certainty" (video)