Pierre-Joseph Proudhon, Justice in the Revolution and in the Church, Volume I, “Program,” section V.
§ V. — That metaphysics is within the province of primary instruction.
The definition of philosophy implies by its terms: 1) someone who seeks, observes, analyzes, synthesizes and discovers, which we call the Subject or Moi; 2) something which is observed, analyzed, the reason of which we seek, and which we call the Object or Non-moi.
The first – the observer, subject, moi, or mind – is active; the second – the thing observed, object, non-moi, or phenomenon – is passive. Let us not frighten ourselves with words: this means that the one is the artisan of the idea, and that the other furnishes their material. There is no statue without the sculptor: this is very simple, is it not? But neither is there a statue without the marble: this is also clear. Now, it is thus for ideas. Suppress one or the other of these two principles, the subject or the object, and no idea will be formed; thought will no longer be possible. Philosophy vanishes. Suppress the sculptor or the block of marble, and you will have no statue. Every artistic or industrial production is like this. Remove the worker, you will remain eternally with your raw materials; remove the materials from the works, and if your ask him to produce anything by his thought alone, he will think that you are mocking him.
However, in this competition, or this opposition, of the subject and object, of the mind and things, we want to know in a more precise manner what is the role of each; in what consists the action of the mind, and what are the natures of the materials he puts to work.
The mind or the moi is, or at least it acts as if it is, prone to affirm itself as a simple and indivisible nature, consequently as if it is more penetrating and impenetrable, more active and less corruptible, more prompt and less subject to change. Things, on the contrary, appear extended and composite, consequently divisible, successive, variable, penetrable, subject to dissolution, susceptible to a greater or lesser degree in all their qualities and properties.
How the mind, put in relation with external objects by the intermediary of the senses, perceives a nature so  different from itself is what seems at the first abord inexplicable. Can the simple see the composite? That repels us. On reflection, however, we recognize this it is precisely that difference of nature which renders objects perceptible to the mind, and subjects them to it. For it sees them, remark it well, not in their substance, which it cannot conceive as other than simple (atomistic), after its own example, and which consequently escapes it; it sees them in their composition and their differences. The intuition of the mind, its action on objects, comes thus from two causes: by its acuity, it divides them and differentiates them infinitely; then, by its simplicity, it restores all these diversities to unity. What the mind sees in things is their differences, species, series and groups, in a word their reason, and it is because it is mind, because it is simple in its essence, that is sees all that. What the mind cannot discover is the nature or the in itself of things, because that nature, laid bare of its differences, of its unity of composition, etc., becomes then like the mind itself, something simple, amorphous, unapproachable and invisible.
The consequence of all this is easy to grasp. The mind put in the presence of things, the moi in communication with the non-moi, in receipt of impressions and images; it grasps differences, variations, analogies, groups, genera, species: all that is the fruit of its first perception. But the mind does not stop there; and the representation of things would not be complete in its thought, it would lack basis and perspective, if the mind did not add something more of its own.
In seeing then that infinite diversity of things, such a diversity that each thing seems to denounce itself as having been able to be completely different than it is, the mind, which feels itself single, in opposition to things, conceives the One, the Identical, the Immutable, which is not to be found;
In observing the contingency of phenomena, the mind conceives the Necessary, which it does not find either: lucky, if it did not decide to adore it under the name of Destiny!
In taking the comparative dimensions of objects and establishing their limits, it conceives Infinity, which is no more real; 
In following, in its consciousness, the revolutions of time, and measuring the duration of existences, it conceives the Eternal, which cannot be said of any person or any thing;
In recognizing the mutual independence of creatures, it conceives of itself as superior to the creatures, and affirms it Free Will and his Sovereignty, of which nothing can yet give it the model;
In seeing movement, it conceives of Inertia, a hypothesis without reality; in calculating speed, it conceives of force, which it never grasps;
In noting the action of being on one another, it conceives of Cause, in the analysis of which it only grasps a contradiction;
In comparing the faculties of some to the faculties of others, it conceives of Life, Intelligence and Soul; and by opposition, Matter, Death and Nothingness: abstractions or fictions? it does not know;
In classing and grouping creatures according to their genera and species, it conceives the Universal, superior to every collectivity;
In calculating the relations of things, it conceives of Law, the notion of which immediately gives it that of an Order of the world, although there has been struggle everywhere,and consequently as much disorder as order;
Finally, in condemning, according to the purity of its essence, all that appears to it out of proportion, small, mean, monstrous, discordant and deformed, it conceives the Beautiful and the Sublime, in a word the Ideal, which it is condemned to follow always, without ever enjoying it.
All these conceptions of the mind, famous in the School under the name of the categories, are indispensables for the understanding of things; reasoning is impossible without them: while they do not result from sensation, since, as we see, they exceed sensation, the perceived image, by all the distance from the finite to infinity. What they take from sensation are the various points which have served to form them antithetically; the point of view of diversity, of contingency, of the limit, etc. Except, the categories or conceptions of reason all merge in with one another; they are adequate to one another and  imply each other mutually, since all are invariably related, not to things, but to the essence of mind, which is single and incorruptible…..
The formation of the categories or ideas, conceived by the mind apart from experience but on the occasion of experience, their collection and classification, forms what we call metaphysics. It is entirely in grammar, and its teaching belongs to the schoolmasters.
From the manner in which the categories form, and from their usage in language and in the sciences, it results that, as analytic or synthetic signs, they are the condition sine qua non of speech and of knowledge, that they form the instrumentation of intelligence, but that by themselves they are sterile, and consequently that metaphysics, excluding, by its nature and destination, all positivism, can never become a science.
All science is essentially metaphysical, since every science generalizes and distiguishes. Every man who knows, however little he knows, every man who speaks, provided that he understands, is a metaphysician; just as every man who seeks the reason of things is a philosopher. Metaphysics is the first thing that infants and savages think: we could even say that in the mind of every man, metaphysics is present in inverse proportion to science.
Thus, by what fanaticism of abstraction can a man call himself exclusively a metaphysician, and how, in a knowledgeable and positive century, do professors of pure philosophy still exist, these people who teach the young to philosophize apart from all science, all art, all literature and all industry, people, in a word, making a trade, the most consciensciously in the world, of selling the absolute?
Those who should once understand the theory of the formation of ideas, and who will carefully take into account these three capital points: 1) the intervention of two agents, the subject and the object, in the formation of knowledge; 2) the difference in their roles, resulting from the difference in their natures; 3) the distinction of ideas into two species, sensible ideas given immediately by objects, and  extra-sensible or metaphysical ideas, resulting from the action of the mind solicited by the contemplation of the outside; that one, we say, can boast of having taken the most difficult step of philosophy. He is freed from fatalism and from superstition. He knows that all his ideas are necessarily posterior to the experience of things, metaphysical ideas as well as sensible ideas; he will remain unshakably and forever convinced that, just as adoration, prophecy, the gift of tongues and of miracles, somnambulism, idealism, whether subjective, objective or absolute, and all the practices of the great work of alchemy, has never produced for indigent humanity an ounce of bread, has created neither shoes, not hats, nor shirts; so it will not have added an iota to knowledge. And il will conclude with the great philosopher Martin, in Candide: “We must cultivate our garden.” The garden of the philosopher is the spectacle of the Universe. Verify unceasingly your observations; put your ideas in order; take care in your analyses, your recapitulations, your conclusions; be sober in your conjectures and hypotheses; mistrust probabilities and above all authorities; do not believe the word of any soul who lives, and use the ideal as a means of scientific construction and control, but do not worship it. Those who, all all times, have claimed detach science from all empiricism and to raise the edifice of philosophy on metaphysical ideas alone, have only succeeded in making themselves plagiarists of the ancient theology. Their counterfeits have fallen on their own heads; their transcendentalism has brought to ruin the supernatural in which the people have at all times believed, and they have managed to lose what they wanted to save. Remember, finally, that there is no more innate or revealed science than there are innate privileges or wealth fallen from heaven; and that, as all well-being must be obtained by labor, or be theft, so all knowledge must be the fruit of study, or be false.
- The coming of the people to philosophy
- The definition of philosophy
- On the quality of the philosophical mind
- The origin of ideas
- That metaphysics is within the province of primary instruction
- That philosophy must be essentially practical (next)
- The character that must be presented by the guarantee of our judgments and the rule of our actions.–Conversion from speculative to practical reason: determination of the criterion.
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