These two groups, on the whole, correspond with the two different principal forms of the human notions of the universe which we have already contrasted as the _monistic and the dualistic_ conception of nature. In the usual dualistic or teleological (vital) conception of the universe, organic nature is regarded as the purposely executed production of a Creator working according to a definite plan. Its adherents see in every individual species of animal and plant an “embodied creative thought,” the material expression of a _definite first cause_ (causa finalis) acting for a set purpose. They must necessarily assume supernatural (not mechanical) processes for the origin of organisms. With justice, we may therefore designate their scheme of the world’s growth as the _Supernatural History of Creation_. Among all such teleological histories of creation, that of Moses has gained the greatest influence, since even so distinguished a naturalist as Linnæus has claimed admittance for it in Natural Science. Cuvier’s and Agassiz’s views of creation also belong to this group, as do in fact those of the great majority of both scientific and unscientific men. On the other hand, the theory of development carried out by Darwin, which we shall have to treat of here as the _Non-miraculous_ or _Natural History of Creation_, and which has already been put forward by Goethe and Lamarck, must, if carried out logically, lead to the monistic or mechanical (causal) conception of the universe. In opposition to the dualistic or teleological conception of nature, our theory considers organic, as well as inorganic, bodies to be the necessary products of natural forces. It does not see in every individual species of animal and plant the embodied thought of a personal Creator, but the expression for the time being of a mechanical process of development of matter, the expression of a necessarily active cause, that is, of a mechanical cause (causa efficiens). Where teleological Dualism seeks the arbitrary thoughts of a capricious Creator in the miracles of creation, causal Monism finds in the process of development the necessary effects of eternal immutable laws of nature. The Monism here maintained by us is often considered identical with Materialism. Now, as Darwinism, and in fact the whole theory of development, has been designated as “_materialistic_,” I cannot avoid here at once guarding myself against this ambiguous word, and against the malice with which, in certain quarters, it is employed to stigmatize our doctrine.