Pierre-Joseph Proudhon, Justice in the Revolution and in the Church, Volume I, "Program," section III.
§ III. — On the quality of the philosophical mind.
But here is a rather different affair! It is a question of knowing if philosophy, of which it was first said that the people were incapable, will not, by its very practice, create inequality among men. What can we conclude from our definition?
Since philosophy is the search for, and, so far as it is possible, the discovery of the reason of things, it is clear that, in order to philosophize well, the first and most necessary condition is to is to observe things carefully; to consider them successively in all their parts and all their aspects, without permitting oneself a notion of the ensemble before being certain of the details. This is the precept of Bacon and Descartes, the two fathers of modern philosophy. Couldn't one say that in expounding it, they thought especially of the people? Philosophy is all in the observation, internal and external: there is no exception to that rule.
The philosopher, the man who seeks, who still does not know, can be compared to a navigator charged with making a map of an island, and who, in order to carry out his mission, being unable to take a photograph of the country from high in the atmosphere, is obliged to follow with attention, and to record one after another on paper, with exactitude, all the sinuosities and crevices of the coast. The circumnavigation completed, and the summary of observations finished, the geographer would have obtained as faithful a representation as possible of the island, in its parts and in the ensemble, which he never could have done, if, holding himself at a distance, he had been limited to drawing perspectives and landscapes.
The philosopher can also be compared to a traveler who, after having traversed in all directions a vast plain, having recognized and visited the woods, the fields, the meadows, the vineyards, the habitations, etc., would then climb a mountain. As he made his ascent, the objects would pass again before his eyes in a general panorama, which would  make him understand that of which the inspection of the details had only given him an incomplete idea.
Thus, must stick close to the facts and constantly refer to them, divide his material, make complete counts and exact description. He must go from simple notions to the most comprehensive formulas, testing his views of the ensemble and the glimpsed details against one another. Finally, where immediate observation becomes impossible, to show himself sober in his conjectures, circumspect with regard to probabilities, to challenge analogies, and to judge only self-consciously, and always with reserve, distant things by those near, the invisible by the visible. -- Under these conditions, would it be too much to say that the practical man is closer to the truth, less subject to illusion and to error than the speculative one? Regular contact with things preserves him from fantasy and vain systems: if the practitioner shines little from invention, he also courts less risk of making a mistake, and rarely loses by waiting. He who works prays, says an old proverb. Can we not also say: He who works, in so far as he pays attention to his work, philosophizes?
It is only by following this scrupulous and slowly rising method of observation, that the philosopher could flatter flatter himself to have reached the summit of philosophy, science, the condition of which is double, certainty and synthesis. These words should frighten no one: here again the most transcendent philosophy contains nothing outside the abilities and reach of the people.
Indeed, a man may have seen more of things than is common among his fellows; he may have viewed them in more detail and more closely; he can thus consider them from a higher level and in a larger ensemble: this question of quantity, which has no influence on the quality of the knowledge, adds nothing to the certainty, and consequently does not increase the value of the mind. This is of extreme importance for the determination of personal right, constitutive of society: allow me to clarify my thought with some examples.
2 multiplied by 2 equals 4: this is, for everyone, a perfect certainty. But how much is 27 multiplied by 23? Here, more than one innocent will hesitate, and  if he has not learned to calculate by figures, it will take a long time to find the solution, let alone dare to respond. Thus I take up the pen, and making the multiplication, I respond that the product demanded is 621. Now, knowing so easily the product of 27 times 23, and being able with the same promptitude and sureness to make the multiplication of all the possible numbers by all the possible numbers, I am clearly more knowledgeable that the one whose arithmetic capacity will stop at the elementary operation 2 x 2 = 4. Does this make me more certain? Not at all. The quantity of knowledge, I repeat, adds nothing to the philosophical quality of the knowing: it is by virtue of that principle, and another just like in that we will speak of below, that French law, coming out of the Revolution of 89, has declared us all equal before the law. Between two citizens, between two men, there can be inequality of acquired knowledge, of effective labor, of services rendered; there is no inequality of the quality of reason: such is, in France, the foundation of personal right, and such is the basis of our democracy. The old regime did not reason in the same way: is it clear now that philosophy is the legacy of the people?
It is the same for the comprehensive power of the mind.
2 multiplied by two produces 4, and 2 added to 2 still gives 4: on one side the product, on the other the sum are equal. However little the innocent to whom one makes the remark reflects on it, he will realize that addition and multiplication, although they begin from two different points of view and proceed in two different manners, resolve themselves, in this particular case, in an identical operation. By making a new effort, he will comprehend as well that 2 minus 4 or 4 divided by 2, it always remains 2, as subtraction and division still resolve, in this particular case, into one single and same operation. All this will interest, and perhaps astonish him: he will have, in the measure from 2 to 4, a synthetic view of things. But the arithmetician knows much more, and his synthesis is incomparably more comprehensive. He knows that whenever one operates on numbers larger than 2, the results can no longer be the same; that multiplication is an abbreviated addition, and division an abbreviated subtraction as well; that  more, subtraction is the opposite of addition, and division the opposite of multiplication; in summary, that all these operations, and others more difficult which are deduced from them, come down to the art of composing and decomposing the series of numbers. Does this give him the right to believe himself superior to the other, in nature and dignity? Certainly not: the only difference is that one has learned more than the other; but reason is the same for both of them, and this is why the legislator, at once a revolutionary and a philosopher, has decided that he will take no account of persons. It is for this reason, finally, that modern civilization tends invincibly to democracy: where philosophy reigns, where as a consequence the identity of philosophical reason is recognized, the distinction of classes, like the hierarchy of church and State, is impossible.
We can make analogous arguments about all of the genres of knowledge, and we will always arrive at that decisive conclusion, that, for whoever knows, certainty is of the same quality and degree, despite extend of the knowledge; just as, for whoever grasps the relation of several objects or ideas, the synthesis is of the same quality and form, despite the multitude relations grasped. In no case will there be room to distinguish between the reason of the people and the reason of the philosopher.