 Our interpretation of this change in attention to classes and relations indicated by the shift in notation is that it indicates the extent to which the solution to the paradoxes, which required a ramified theory of (possibly intensional) propositional functions, may have superseded a logic based on an unproblematic notion of class and mathematical functions and relations between them, that appeared in the body of The Principles of Mathematics before Russell’s attention was drawn to the paradoxes. In the summary of the later sections of PM that follows below, it will appear that in fact the symbolic development follows very closely that of PoM from ten years earlier. While we do not know much about the order in which sections of PM were composed, it will appear from this change of attention from propositional functions to classes and relations, that the later parts are in fact an earlier stratum in the conceptual development of the project that started out as a symbolic “Volume II” to follow PoM.