A funny thing happened on the way to "property is theft!" In the Second Memoir on property (1841), Proudhon explained the course of study that led him, somewhat indirectly, to his work on property:
By taste as well as by discretion and lack of confidence in my powers, I was slowly pursuing some commonplace studies in philology, mingled with a little metaphysics, when I suddenly fell upon the greatest problem that ever has occupied philosophical minds: I mean the criterion of certainty.Those of my readers who are unacquainted with the philosophical terminology will be glad to be told in a few words what this criterion is, which plays so great a part in my work.The criterion of certainty, according to the philosophers, will be, when discovered, an infallible method of establishing the truth of an opinion, a judgment, a theory, or a system, in nearly the same way as gold is recognized by the touchstone, as iron approaches the magnet, or, better still, as we verify a mathematical operation by applying the proof. Time has hitherto served as a sort of criterion for society. Thus, the primitive men—having observed that they were not all equal in strength, beauty, and labor—judged, and rightly, that certain ones among them were called by nature to the performance of simple and common functions; but they concluded, and this is where their error lay, that these same individuals of duller intellect, more restricted genius, and weaker personality, were predestined to serve the others; that is, to labor while the latter rested, and to have no other will than theirs: and from this idea of a natural subordination among men sprang domesticity, which, voluntarily accepted at first, was imperceptibly converted into horrible slavery. Time, making this error more palpable, has brought about justice. Nations have learned at their own cost that the subjection of man to man is a false idea, an erroneous theory, pernicious alike to master and to slave. And yet such a social system has stood several thousand years, and has been defended by celebrated philosophers; even to-day, under somewhat mitigated forms, sophists of every description uphold and extol it. But experience is bringing it to an end.Time, then, is the criterion of societies; thus looked at, history is the demonstration of the errors of humanity by the argument reductio ad absurdum.Now, the criterion sought for by metaphysicians would have the advantage of discriminating at once between the true and the false in every opinion; so that in politics, religion, and morals, for example, the true and the useful being immediately recognized, we should no longer need to await the sorrowful experience of time. Evidently such a secret would be death to the sophists,—that cursed brood, who, under different names, excite the curiosity of nations, and, owing to the difficulty of separating the truth from the error in their artistically woven theories, lead them into fatal ventures, disturb their peace, and fill them with such extraordinary prejudice.Up to this day, the criterion of certainty remains a mystery; this is owing to the multitude of criteria that have been successively proposed. Some have taken for an absolute and definite criterion the testimony of the senses; others intuition; these evidence; those argument. M. Lamennais affirms that there is no other criterion than universal reason. Before him, M. de Bonald thought he had discovered it in language. Quite recently, M. Buchez has proposed morality; and, to harmonize them all, the eclectics have said that it was absurd to seek for an absolute criterion, since there were as many criteria as special orders of knowledge.Of all these hypotheses it may be observed, That the testimony of the senses is not a criterion, because the senses, relating us only to phenomena, furnish us with no ideas; that intuition needs external confirmation or objective certainty; that evidence requires proof, and argument verification; that universal reason has been wrong many a time; that language serves equally well to express the true or the false; that morality, like all the rest, needs demonstration and rule; and finally, that the eclectic idea is the least reasonable of all, since it is of no use to say that there are several criteria if we cannot point out one. I very much fear that it will be with the criterion as with the philosopher’s stone; that it will finally be abandoned, not only as insolvable, but as chimerical. Consequently, I entertain no hopes of having found it; nevertheless, I am not sure that some one more skilful will not discover it.Be it as it may with regard to a criterion or criteria, there are methods of demonstration which, when applied to certain subjects, may lead to the discovery of unknown truths, bring to light relations hitherto unsuspected, and lift a paradox to the highest degree of certainty. In such a case, it is not by its novelty, nor even by its content, that a system should be judged, but by its method. The critic, then, should follow the example of the Supreme Court, which, in the cases which come before it, never examines the facts, but only the form of procedure. Now, what is the form of procedure? A method.I then looked to see what philosophy, in the absence of a criterion, had accomplished by the aid of special methods, and I must say that I could not discover—in spite of the loudly-proclaimed pretensions of some—that it had produced any thing of real value; and, at last, wearied with the philosophical twaddle, I resolved to make a new search for the criterion. I confess it, to my shame, this folly lasted for two years, and I am not yet entirely rid of it. It was like seeking a needle in a haystack. I might have learned Chinese or Arabic in the time that I have lost in considering and reconsidering syllogisms, in rising to the summit of an induction as to the top of a ladder, in inserting a proposition between the horns of a dilemma, in decomposing, distinguishing, separating, denying, affirming, admitting, as if I could pass abstractions through a sieve.
I selected justice as the subject-matter of my experiments. Finally, after a thousand decompositions, recompositions, and double compositions, I found at the bottom of my analytical crucible, not the criterion of certainty, but a metaphysico-economico-political treatise, whose conclusions were such that I did not care to present them in a more artistic or, if you will, more intelligible form. The effect which this work produced upon all classes of minds gave me an idea of the spirit of our age, and did not cause me to regret the prudent and scientific obscurity of my style.
I'll be posting a couple more sections touching on this same problem, which occupied a surprisingly central place in Proudhon's thought. It was, of course, the central concern of the 1853 Philosophy of Progress.