But just as there are some wants of the body which every one has to satisfy by himself, so every one has to know certain scientific facts which are not the prerogative of any special science.
This is true of the faculty of human understanding. The knowledge and study of this theory cannot be left to any particular guild. Lassalle justly says: "Thinking itself has become a special trade in these days of division of labor, and it has fallen into the worst hands, those of our newspaper writers." He thus urges us not to acquiesce in this appropriation any longer, not to submit any more to the harangues of public opinion, but to resume thinking for ourselves. We may leave certain objects of scientific research to professionals, but general thought is a public matter which every one should be required to attend to himself.
If we could place this general work of thinking on a scientific basis, if we could find a theory of general thought, if we were able to discover the means by which reason arrives at understanding, if we could develop a method by which truth is produced scientifically, then we should acquire for science in general and for our individual faculty of judgment the same certainty of success which we already possess in special fields of science.
Kant says: "If it is not possible to harmonize the various co-operators on the question of the means by which their common aim is to be accomplished, then we may safely infer that such a study is not yet on the secure road of science, but will continue to grope in the dark."
Now, if we take a look at the sciences, we find that there are many, especially among the natural sciences, which fulfill the requirements of Kant, agreeing unanimously and consciously on certain empirical knowledge and building further understanding on that. "There we know," as Liebig says, "what is to be called a certain fact, a conclusion, a rule, a law. We have touchstones for all this, and every one makes use of them before making known the fruits of his labors. The attempt to maintain any proposition by lawyer's tricks, or the intention to make others believe anything that cannot be proven, are immediately wrecked by the ethics of science."
Not so in other fields, where concrete and material things are left behind and abstract, so-called philosophical, matters are taken up, as, for instance, questions of general conceptions of the world and of life, of beginning and end, of the semblance and the essence of things, of cause and effect, of matter and force, of might and right, of wisdom of life, of morality, religion, and politics. Here we find, instead of irrefutable proofs, mere "lawyer's tricks," an absence of reliable knowledge, a mere groping amid contradictory opinions.
And it is precisely the prominent authorities of natural science who show by their disagreements on such matters that they are mere tyros in philosophy. It follows, then, that the socalled ethics of science, the touchstones of which the boast is made that they never fail in determining what is knowledge and what is mere conjecture, are based on a purely instinctive practice, not on a conscious theory of understanding. Although our time excels in diligent scientific research, yet the numerous differences among scientists show that they are not capable of using their knowledge with a predetermined certainty of success. Otherwise, how could misunderstandings arise? Whoever understands understanding, cannot misunderstand. It is only the absolute accuracy of astronomical computations which entitles astronomy to the name of a science. A man who can figure is at least enabled to test whether his computation is right or wrong. In the same way, the general understanding of the process of thought must furnish us with the touchstone by which we can distinguish between understanding and misunderstanding, knowledge and conjecture, truth and error, by general and irrefutable rules. Erring is human, but not scientific. Science being a human matter, errors may exist eternally, but the understanding of the process of thought will enable us quite as well to prevent errors from being offered and accepted as scientific truths as an understanding of mathematics enables us to eliminate errors from our computations.
It sounds paradoxical and yet it is true: Whoever knows the general rule by which error may be distinguished from truth, and knows it as well as the rule in grammar by which a noun is distinguished from a verb, will be able to distinguish in both cases with equal certainty. Scientists as well as scribes have ever embarrassed one another by the question: What is truth? This question has been an essential object of philosophy for thousands of years. This question, like philosophy itself, is finally settled by the understanding of the faculty of human thought. In other words, the question of what constitutes truth is identical with the question of the distinction between truth and error. Philosophy is the science which has been engaged in solving this riddle, and the final solution of the riddle by the clear understanding of the process of thought also solves the question of the nature of philosophy. Hence a short glance at the nature and development of philosophy may well serve as an introduction to our study.
As the word philosophy is connected with various meanings, I state at the outset that I am referring only to socalled speculative philosophy. I dispense with frequent quotations and notes of the sources of my knowledge, as anything that I may say in this respect is so well established that we can afford to discard all scientific by-work.
If we apply the above-named test of Kant to speculative philosophy it appears to be more the playground of different opinions than of science. The philosophical celebrities and classic authorities are not even in accord on the question: What is philosophy and what is its aim? For this reason, and in order not to increase the difference by adding my own opinion, I regard everything as philosophy that calls itself by that name, and we select from the voluminous literature of philosophy that which is common and general in all philosophers, without taking any notice of their special peculiarities.