Old line metaphysical logic was so enamored of its object that the descent, the kinship, and the connection with the common things of this world seemed too ordinary for the exquisite spirit. That logic was transcendental, and therefore its chosen object likewise had to be in touch with a transcendental world. And though it was scientific enough to regard the tale of the creation of the first soul by the breath of God as a fable, it was nevertheless so prejudiced in favor of the extraordinary nature of the intellect that it did not abandon, for thousands of years, the hope of finding in that intellect a source which would reveal transcendental matters. Formal logic now entirely discards this hope of a fantastical world, but at the same time it misunderstands the natural connection between the spirit and the common world. It isolates the instrument of thought and leaves the question undecided whether this instrument has a natural, supernatural, or no connection at all. It overlooks that just as logic is real, so reality is logical, and does not see that the back door which leads to illogical heaven by way of faith deserves the disdain of science.
Thought, intellect, are really existing, and their existence is a uniform part of the universal existence. That is the cardinal point of sober logic.
The fact that the thoughts are of the same worldly substance as the other parts of the universe, that they are parts of common nature and not a transcendental essence, has already been expressed by Cartesius in the famous words: "Cogito, ergo sum," I think, therefore I am.
The fact of my thinking, says the philosopher, proves my existence. In order to come to an absolute conviction on the nature of truth and error, he sets out by doubting everything. And then he says that he cannot doubt the existence of his thoughts. He thus placed the spirit on the basis of real life, delivered it of its transcendentalism, and that constitutes his everlasting merit.
However, not alone Cartesius, but also your own experience testifies to the inseparable connection between thinking and being. Have not your thoughts been connected always and everywhere with some worldly or real object? If you attempt to isolate thought in order to ponder over it, you can only do so because that thought has been experienced by you and therefore was in every instance attached to some worldly object. True, you have thought of Greek gods, brownies, and mermaids. But you, an amateur in painting, are familiar enough with that part of the mind which is called imagination in order to admit that even this eccentric part of the mind does not only act, and therefore, exist in reality, but also derives all its products from reality, so that even its most fantastical vagaries and illusions are still real pictures, reflections of reality.
But how is it that I require such a multitude of words in order to state over and over again that the thought has a real existence and is a uniform part of the universe? Simply because from time immemorial the confusion in matters of logic is so great that the human spirit is in the same breath exalted to heaven, and yet its thoughts regarded as nothing real, nothing true. This is made plain by the fact that a sharp distinction is commonly made between that which is real and that which is only imagined, and this difference is exaggerated to such an extent that it appears as if the idea, which indeed is only in the brain, has no real existence at all.
In order that you may understand the interrelations of the things of the universe, I must warn you against this exaggeration and prove that the intellect has a real existence which is connected with the universe or reality. Botany, which occupies itself with plants, does not only teach us to divide them into classes, orders, and families, but it also does more by showing us what place in the entire realm of nature is occupied by the vegetable kingdom, by pointing out the differences which distinguish the plants from the inorganic mineral kingdom or the organic animal kingdom. Formal logic similarly dissects the spirit into its parts, makes distinctions between conceptions, ideas, judgments, conclusions, divides these into subdivisions, classifies conceptions according to species, separates abstract and concrete thought, knows many varieties of judgments, registers three, four, or more modes of conclusion. But at the same time this formal logic recoils from touching on the question as to how the universal spirit is related to the universe, what role it plays in the general existence, whether it is part and parcel of nature or transcendental. And yet this is the most interesting part, the part which logically connects the intellect and the science of the intellect with all other sciences and things.
Logic must teach us how to distinguish. It is not a question, however, of distinguishing sheet iron from gold, or a greyhound from a pug-dog, for this is done by special lines of knowledge. Logic must rather enlighten us about that part of the faculty of distinguishing which is generally required in all branches of knowledge, whereby truth and error, imagination and reality are recognized. To this end I feel impelled to advise you not to overlook that even error and imagination belong to the one infinite and absolutely coherent reality. For the purpose of distinguishing true imagination from actual reality, it must be remembered that just as rye bread and cream puffs agree in belonging to the general category of baker's products, so imagination and truth, thought and reality, are two different kinds of the same nature.
To sum up the contents of this letter, let me point out that its beginning shows the connection of the intellect with the development of the people, while its conclusion explains the wider connection of the mind with the universal existence.