What I propose to do here is to specify how this book is to be read so as to be understood. – It aims to convey a single thought. But in spite of all my efforts, I could not find a shorter way of conveying the thought than the whole of this book. – I believe it is the idea that people have sought out for such a long time under the heading of philosophy, which is why scholars of history have thought it to be as impossible to discover as the philosophers' stone, although Pliny had already told them: ‘how much has been considered impossible before it has been done?’ (Natural History, 7, 1).

As this one thought is considered from different sides, it reveals itself respectively as what has been called metaphysics, what has been called ethics, and what has been called aesthetics; and it is only natural that it be all of these, if it really is what I claim it to be.

A system of thoughts must always have an architectonic coherence, i.e. a coherence in which one part always supports another without the second supporting the first, so the foundation stone will ultimately support all the parts without itself being supported by any of them, and the summit will be supported without itself supporting anything. A single thought, on the other hand, however comprehensive it might be, must preserve the most perfect unity.