 The Extremal Condition: There must be no better way of accounting for the a priori covariance: no better account, other than according best opinion an extension-determining role, of which the satisfaction of the foregoing three conditions is a consequence. (Justification: without this condition, the satisfaction of the foregoing conditions would be consistent with the thought that certain states of affairs are judgement-independent even though infallibly detectable, “states of affairs in whose determination facts about the deliverances of best opinions are in no way implicated although there is, a priori, no possibility of their misrepresentation” (Wright 1992: 123).)