Modern conscious speculation takes its departure from the experienced difference between semblance and truth. It denies all sense phenomena in order to find truth by thinking, without being deceived by any semblance. The subsequent philosophers, however, found every time that the truths of their predecessors, gained by this method, were not what they pretended to be, but that their positive result consisted simply in having advanced the science of the thought process to a certain extent. By denying the actuality of the senses, by endeavoring to separate thought from all sense perceptions, by isolating it, so to say, from its sensory cover, speculative philosophy, more than any other science, laid bare the structure of the mind. The more this philosophy advanced in time, the more it developed in its historical course, the more classically and strikingly did this kernel of its work spring into view. After the repeated creation of giant fantasmagorias, it found its solution in the positive knowledge that socalled pure philosophical thought, abstracting from all concrete contents, is nothing but thoughtless thought, thought without any real object back of it, and produces mere fantasmagorias. This process of speculative deception and scientific exposure was continued up to recent times. Finally the solution of the main question, and the solution of speculation, was introduced with the following words of Feuerbach: "My philosophy is no philosophy." The long story of speculative work was finally reduced to the understanding of reason, of the intellect, the mind, to the exposure of those mysterious operations which we call thinking. The secret of the processes by which the truths of understanding are produced, the ignorance of the fact that every thought requires an object, a premise, was the cause of the idle speculative wanderings which we find registered in the history of philosophy. The same secret is today the cause of those numerous speculative mistakes which we observe in passing over the words and works of naturalists. Their knowledge and understanding is far developed, but only so far as it refers to tangible objects. The moment they touch upon abstract discussions, they offer "lawyers' proofs" in place of "objective facts." For although they know intuitively and in a concrete case that this is a truth, that a conclusion, and that a rule, they do not apply this knowledge in general with consciousness and theoretical consistency. The successes of natural science have taught them to operate the instrument of thought, the mind, instinctively. But they lack the systematic understanding which operates with conscious and predetermined certainty. They ignore the outcome of speculative philosophy.