I. Haeckel and His Opponents

The essence of Monism consists in the assumption that all occurrences in the world, from the simplest mechanical ones upwards to the highest human intellectual creations, evolve themselves naturally in the same sense, and that everything which is called in for the explanation of appearances, must be sought within that same world. Opposed to this view stands Dualism, which regards the pure operation of natural law as insufficient to explain appearances, and takes refuge in a reasoning being ruling over the appearances from above. Natural science, as has been shown, must reject this dualism.