He says, there have ever been two conflicting theories of the universe: the one, monistic; the other, dualistic. The one admits of only one substance, matter; the other of two, matter and mind. He prefers to call the former monism rather than materialism, because the latter term often includes the idea of moral materialism, _i. e._ the doctrine that sensual pleasure is the end of life; a doctrine, he says, much more frequently held by princely church-men than by men of science. He maintains, however, that "all knowable nature is one; that the same eternal, immutable (ehernen, brazen) laws are active in the life of animals and plants, in the formation of crystals, and the power of steam; in the whole sphere of biology, zooelogy, and botany. We have, therefore, the right to hold fast the monistic and mechanical view, whether men choose to brand the system as Materialism or not. In this sense, all natural science, with the law of causation at its head, is thoroughly materialistic." (p. 32) The monistic theory he calls "mechanical or causal," as distinguished from the dualistic theory, which he calls "teleological or vitalistic." According to the latter, "the vegetable and animal kingdoms are considered as the products of a creative agency, working with a definite design. In looking on an organism, the conviction seems unavoidable that so skilfully constructed a machine, such a complicated working apparatus, as an organism is, could be produced only by an agency analogous to, although far more perfect than the agency of man." "This," he says, "supposes the Creator to be an organism analogous to man, although infinitely more perfect; who contemplates his formative powers, lays the plan of the machine, and then, by the use of appropriate means, produces an effect answering to the preconceived plan.... However highly the Creator may be exalted, this view involves the ascription to Him of human attributes, in virtue of which he can form a plan, and construct organisms to correspond with it. That is the view to which Darwin's doctrine is directly opposed, and of which Agassiz is, among naturalists, the most important advocate. The famous work of Agassiz, 'Essay on Classification,' which is in direct opposition to Darwin's, and appeared about the same time, has carried out logically to the utmost the absurd anthropomorphic doctrine of a Creator." (p. 17) The monistic theory is called "mechanical and causal," because it supposes that all the phenomena of the universe, organic and inorganic, vegetable and animal, vital and mental, are due to mechanical or necessarily operating causes (causae efficientes); just as the dualistic theory is called "teleological or vitalistic," because it refers natural organisms to causes working for the accomplishment of a given end (causae finales). (p. 67)