The postulate of equipollence is the main argument of Pyrrhonian sceptics who assert the equality of current positive beliefs about the world with regard to being convincing or unconvincing. In sceptical reasoning, suspension of judgement follows from the manifest absence of an ultimate point of reference. Several major exponents of the Cambridge School have championed a sceptical approach to the history of political thought. They assert the equipollence of competing interpretations of the intentions of historical thinkers and eschew facile conclusions. They also claim that their insights can be brought to bear politically. The latter claim, however, seems to presuppose a set of convictions which sceptics generally do not hold. Drawing on the theory of critical rationalism I discuss whether the retrenchment of the possibility of certain historical knowledge carried out by the authors of the Cambridge School narrows the scope of political action thus defeating the authors’ own claim to be engaged in the furthering of critical reason.