My Dear Son:

After the third letter had acquainted you with the fact that the subject of logic has a certain religious flavor, the two subsequent letters endeavored to show that the logical subject is interconnected with the universal existence of the world, that the faculty of thought is an inseparable part of actual truth. In the vernacular of theology my last two letters have represented the human mind as a part of the living true God.

Christianity teaches: God is a spirit and who would worship him must worship in spirit and in truth.

And logic teaches: The spirit is a part of universal existence. Whoever worships the spirit, is an idolator, for he worships a part and misunderstands the whole truth. Truth itself is identical with the universal existence, with the world, and all things are simply forms, phenomena, predicates, attributes, passing expressions of it. The universal existence may be called divine because it is infinite, being the alpha and omega which comprises all things as special truths. The intellect is such a limited part among other special parts of divine truth, and the latter is frequently called world without any bombastic emphasis.

Undoubtedly, every science, profession and trade can say the same thing of its object. The blue sky and the green trees are divine parts. Everything is interrelated and connected. If that were a good reason for not making any subdivisions, every part and description would become endlessly tiresome.

However, the specialty of logic is the cosmic sum of all truths, because it aims at a general elucidation of the nature of the human brain. This purpose is not so well served by an accumulation of other knowledge as by the general understanding of truth.

Logic, which seeks to enlighten the mind for the purpose of scientific thinking, does not so much treat of true conceptions as of the general and absolute conception of truth which is inseparably linked to the infinite universal life.

If you wish to think scientifically, you will first of all strive after clear ideas. And yet your head may be quite clear in regard to everyday things, without getting any nearer to general clearness. Nor is such clearness obtainable by the accumulation of mere special knowledge, for even if you were to grow in wisdom to the end of your days, nevertheless the fountain of wisdom, the universe, is inexhaustible and your brain will remain imperfectly informed or unclear as before. Yea, even the smallest part of the world is so inexhaustible that the most talented can never acquire all the knowledge necessary to understand entirely even the most minute object. The strongest microscope cannot see all there is to see in a drop of water, and the wisest man can never learn all there is to shoemaking.

You can see by all this that the scientific use of our intellect is furthered by special knowledge only in the corresponding details. For this reason it does not satisfy us to have some logicians tell us how many kinds of concepts, judgments and conclusions are contained in our intellect. These are special details of logic. But the thing of first importance for the student of logic is the elucidation of the universal concept of truth, not the accumulation of special truths.

Special truths enlighten the intellect. But the understanding that all specialties are connected with one another by one monad or unit which is truth itself gives us a certain general enlightenment which certainly does not render any special research unnecessary, or take the place of it, but which may well serve as the foundation of all research, which may therefore be called a fundamental assistance.

I may remark in passing that the understanding of logical science is rendered especially difficult by the fact that the unpracticed understands all terms and concepts only in their narrow popular meaning, while the subject matter leads up continually into the widest fields.

When I speak of parts of the world, you must not think merely of geographical parts, but you must think farther until you arrive at the insight that stars and bricks, matter and force, in short all parts of the world are world parts.

The logical difficulty may be principally traced to the lack of familiarity with the comprehensive categories. It will be clear to you that thinking and being, phenomenon and truth, etc., are conceptions of the widest scope. So you may have some difficulty in distinguishing between concepts of truth, and true concepts. And yet this is the same as making a distinction between the general class of herbs and its individual species. The mere intercourse with such comprehensive concepts as truth, existence, universe, is an excellent school of intellectual enlightenment.

Perhaps you may object to the deviation of a science devoted to the special study of the faculty of thought into such fields as existence or truth. But a logic confined to an analysis of the faculty of understanding would be narrow compared to one representing this faculty of understanding at work in real life. If the science of the eye were to treat only of the various parts of the eye without considering the things outside connected with its function, the light, the objects, in short, the vision of the eye, it would be more an anatomy of the eye than a general science of the eye. At all events a science which represents not alone the subjective faculty of vision, but also the living activity of the eye, the objective field of vision inseparable from the subjective faculty, is a far more comprehensive instruction, a higher enlightenment of the human brain.

In my opinion, logic should not so much treat of the analysis of the intellectual subject as of the purpose and object of the faculty of thought, its culture, which is not accomplished by the intellect itself, but by its connection with the world of truth, its interrelation with the universal existence.

What can a logic accomplish which divides thought into analytical and synthetical thoughts, which speaks of inductive and deductive understanding and of a dozen other kinds, but which finally declines to meet the question of the relation of thought and understanding to truth, and fails to indicate what and where is divine truth and how we may arrive at it?

Pilate, the typical sceptic, shrugs his shoulders; the clergymen make a mystery of divine truth; the natural sciences care only for the true conceptions, but naught for the concept of truth; and then the special science of understanding, formal logic, tries to refer its task to philosophy or world wisdom.

I have already pointed out that the titles of the principal works on philosophy indicate that the whole world wisdom turns around the question: How can our brain be enlightened, how can it arrive at truth? The naturalists answer that this can be accomplished by special studies, and they are frequently opposed to philosophical research which makes general truth its main object, and belittle it. You will readily see that this is a mistake when you consider that, to illustrate, a machine or an organism as a whole is still something more than a mere sum of its parts.

No matter how well you may know each single part, yet you will not understand the whole machine or organism by this means alone. The universe is not an aggregation of unorganized parts, but a living process which must be understood not only in its parts but also as a whole. We may pass for the moment the question whether the Milky Way may be dissolved into stars, and whether the stars may become globes like our Earth which may develop plants, animals, and intelligent beings. The thing which is evident is that there is a process of development, that all nature takes part in this movement, that the universe is a whole without end, composed of an infinite number of parts; a coming and going, an eternal transformation, which is always identical with itself and always the same world. What all this would be without our eyes and ears and without the intellect by means of which we use eyes and ears, what the world "in itself" is, that is a senseless and transcendental speculation.

The science of logic must deal only with the actual world which is inseparable from us and from our thoughts.

This world which we hear, see, smell, in which we live and breathe, is the world of truth or the true world. That is a fact. Must I prove this? And how is a fact proven? How do we prove that a peach is a delicious fruit? One goes and eats it. In the same way, you may now go and enjoy life, of course in a rational manner, and I am convinced that your own love of life will tell you that it is proof positive of the truth of the world, of its actuality.

But even in the midst of this actual world there is present an inconsistent element, a human race with a confused logic. This race has been led by various depressing and saddening circumstances to blacken the delicious truth of this world and to look for a transcendental truth in philosophical metaphysics or religious fantasmagorias, both of which are parts of the same stew. The philosophers of misery who make of the world of truth a vain shadow and a miserable vale of sorrow must needs be convinced by logic that the living world is the only true one.

Well, that is not so difficult. But there is a danger of getting into a vicious circle of errors, imitating a snake biting its own tail. I have to prove logically that the world and truth are one and the same thing, before we have come to an agreement as to what is logical truth or true logic. Nevertheless, nature has assisted us. The logic of nature is the true logic by the help of which we can agree. Nothing more is required than a somewhat trained brain.

Take two men having a dispute about truth. One of them says it is one thing, the other that it is something else. So they are arguing about that which is. This last word is a form of the verb to be. Hence in arguing whether the remote nebula in the heavens is a brick or a star, a male or a female, one is always discussing some form of existence. All disputes turn around forms of existence, but existence itself is an undisputable truth.

Have I now still to prove that all existence is of the same category? Are there any stones that do not belong to the category of stones, or any kind of wood which is iron? What would become of reason and language, if such a thing were to be considered? And yet, much that is being said by opponents is of such a nature.

If I have succeeded in convincing you that the universe is the truth, there still remains the special question: What place shall we assign to fantastic ideas, error, and untruth? If the universe is the truth, then everything would be true, and hence it seems contradictory that error and untruth should have a place in truth or in the world. Of this more anon. I shall only point out in passing that untruth may without any contradiction belong to truth, just as weeds are a negation of herbs and still at the same time herbs.

In conclusion I call your attention to the eminently proletarian character of the science of truth. It gives to the working class the logical justification to renounce all clerical and mystic control and to look for salvation in this same world in which divine truth is living.