 If the sceptics have their own counterpart of a criterion of truth, in terms of the notion of plausibility, they must surely regard that notion as beyond dispute if it is to play its allotted role (2.29). Given the importance of correctly identifying the proper basis for one’s decisions and actions, it cannot for the sceptic be merely plausible, but must be certain, that plausibility is the right criterion. Sceptics are thus impaled on a dilemma: their system undermines itself by being either inconsistent (if ‘nothing can be grasped’ is graspable) or ineffectual (if it is not graspable).