I've pulled together some rough translations from Proudhon's The Creation of Order in Humanity with existing translations from the Second Memoir on Property and Justice in the Revolution and in the Church. Together with The Philosophy of Progress, the collected texts cover some of the major stages in Proudhon's treatment of the question of "the criterion of certainty."
I remember really being puzzled, the first time I read the book on Progress, about the extent to which this summary of Proudhon's thought was focused on the question of certainty, and it has taken a long time, even after discovering his claim that the work on property was really a sort of diversion from his primary concern with the criterion of certainty, to come to terms with just how central the question of certainty is to the pursuit of positive anarchy. However, at the same time I was groping towards this understanding of Proudhon's work, I was also approaching the issue of certainty from a number of other directions in my explorations: in my work with the concept of "guaranteeism," in my slow development of Pierre Leroux's idea that it is fear that sends us toward violent extremes, and, of course, in the work on anarchism's "ungovernability." All of the work on the "anarchism of the encounter" really amounts to saying that anarchism, at least as it appears in that Proudhonian "social system," is the means by which we learn to live freely in a world where almost nothing is certain.
The most recent return to the idea of "two-gun mutualism" was another attempt to keep pulling all those various threads a little closer together. If there is a core to my work on anarchism, it is probably pretty close to that oh-so-slowly-developing "two-gun" project.