"History teaches us that a given view has been abandoned in favor of another by all men, or by all competent men, or perhaps by only the most vocal men; it does not teach us whether the change was sound or whether the rejected view deserved to be rejected. Only an impartial analysis of the view in question, an analysis that is not dazzled by the victory or stunned by the defeat of the adherents of the view concerned—could teach us anything regarding the worth of the view and hence regarding the meaning of the historical change."