I present here a system of philosophy, which means a comprehensive, self-contained worldview. It is the result of careful study and reflection on problems that have occupied humanity for millennia. The entire presentation has been condensed into the briefest form for the sake of brevity. I have sighed too often about the breadth and verbosity of philosophical writings to fall into the same mistake. The decisive truths are always simple; they get lost in the endless chatter. I have also made every effort to write in a way that any educated person can follow. However, a large part of this work consists of mathematical explanations, and most people have such respect for them that they close a book as soon as they see formulas. Let the reader not be deterred by this; they can easily skip over such parts, as the most important concepts are understandable without mathematics and only require common sense.

The Verlag der Wissenschaften publishes historical literature by well-known and lesser-known scientific authors. This makes works that have long been out of print accessible again to interested readers. The present book on the questions of space, time, motion, mass, and the nature of the world of appearances is an unaltered, high-quality reprint of the original second edition from 1902.