This philosophy cannot stand before scientific criticism. It seems everywhere arbitrarily restricted by the narrow limits of the insufficient human intelligence. The existence of the universe is opposed to the law of a sufficient cause; infinity and eternity are incomprehensible to our conceptions, which are confined to space and time. The essential nature of force and volition remains inexplicable. We recognize only a subjectively qualified phenomenon in the world; the impelling forces and the real nature of things are withdrawn from our understanding. A systematic explanation of the universe is quite impossible from the human standpoint. So much seems clear--although no demonstrable certainty attaches to this theory--that spiritual laws beyond the comprehension of us men govern the world according to a conscious plan of development in the revolving cycles of a perpetual change. Even the gradual evolution of mankind seems ruled by a hidden moral law. At any rate we recognize in the growing spread of civilization and common moral ideas a gradual progress towards purer and higher forms of life. It is indeed impossible for us to prove design and purpose in every individual case, because our attitude to the universal whole is too limited and anomalous. But within the limitations of our knowledge of things and of the inner necessity of events we can at least try to understand in broad outlines the ways of Providence, which we may also term the principles of development. We shall thus obtain useful guidance for our further investigation and procedure. The agency and will of Providence are most clearly seen in the history of the growth of species and races, of peoples and States. "What is true," Goethe once said in a letter to Zelter, "can but be raised and supported by its history; what is false only lowered and dissipated by its history."