Just as monism, or naturalism, embraces the totality of science, so on our principles the idea of nature comprises the whole scientifically knowable world. In the strict monistic sense of Spinoza the ideas of God and Nature are synonymous for us. Whether there is a realm of the supernatural and spiritual beyond nature we do not know. All that is said of it in religious myths and legends, or metaphysical speculations and dogmas, is mere poetry and an outcome of imagination. The imagination of civilized man is ever seeking to produce unified images in art and science, and when it meets with gaps in these in the association of ideas it endeavors to fill them with its own creations. These creations of the phronema with which we fill the gaps in our knowledge are called _hypotheses_ when they are in harmony with the empirically established facts, and _myths_ when they contradict the facts: this is the case with religious myths, miracles, etc. Even when people contrast mind with nature, this is only a result, as a rule, of similar superstitions (animism, spiritism, etc.). But when we speak of man's mind as a higher psychic function, we mean a special physiological function of the brain, or that particular part of the cortex of the brain which we call the phronema, or organ of thought. This higher psychic function is a natural phenomenon, subject, like all other natural phenomena, to the law of substance. The old Latin word _natura_ (from _nasci_, to be born) stands, like the corresponding Greek term _physis_ (from _phyo_--to grow), for the essence of the world as an eternal "being and becoming"--a profound thought! Hence physics, the science of the _physis_, is, in the broadest sense of the word, "natural science."