This energetic revival of the distinction already common in the Middle Ages between "positive and natural," which Lord Herbert of Cherbury brought forward at the same period (1624) in the philosophy of religion, gave the catchword for a movement in practical philosophy whose developments extend into the nineteenth century. Not only the illumination period, but all modern philosophy down to Kant and Fichte, is under the ban of the antithesis, natural and artificial. In all fields, in ethics as well as in noëtics, men return to the primitive or storm back to it, in the hope of finding there the source of all truth and the cure for all evils. Sometimes it is called nature, sometimes reason (natural law and rational law are synonymous, as also natural religion and the religion of the reason), by which is understood that which is permanent and everywhere the same in contrast to the temporary and the changeable, that which is innate in contrast to that which has been developed, in contrast, further, to that which has been revealed. Whatever passes as law in all places and at all times is natural law, says Grotius; that which all men believe forms the content of natural religion, says Lord Herbert. Before long it comes to be said: that _alone_ is genuine, true, healthy, and valuable which has eternal and universal validity; all else is not only superfluous and valueless but of evil, for it must be unnatural and corrupt. This step is taken by Deism, with the principle that whatever is not natural or rational in the sense indicated is unnatural and irrational. Parallel phenomena are not wanting, further, in the philosophy of law (Gierke, _Althusius_). But these errors must not be too harshly judged. The confidence with which they were made sprang from the real and the historical force of their underlying idea.