But as in his philosophy, so also in the form of his State, he goes far beyond the old Pythagoreans. He attempts a task really impossible, which is to unite the past of Greek history with the future of philosophy, analogous to that other impossibility, which has often been the dream of Christendom, the attempt to unite the past history of Europe with the kingdom of Christ. Nothing actually existing in the world at all resembles Plato's ideal State; nor does he himself imagine that such a State is possible. This he repeats again and again; e.g. in the Republic (ix. _sub fin._), or in the Laws (Book v. 739), where, casting a glance back on the Republic, he admits that the perfect state of communism and philosophy was impossible in his own age, though still to be retained as a pattern. The same doubt is implied in the earnestness with which he argues in the Republic (v. 472 D) that ideals are none the worse because they cannot be realized in fact, and {clxxiv} in the chorus of laughter, which like a breaking wave will, as he anticipates, greet the mention of his proposals; though like other writers of fiction, he uses all his art to give reality to his inventions. When asked how the ideal polity can come into being, he answers ironically, 'When one son of a king becomes a philosopher'; he designates the fiction of the earth-born men as 'a noble lie'; and when the structure is finally complete, he fairly tells you that his Republic is a vision only, which in some sense may have reality, but not in the vulgar one of a reign of philosophers upon earth. It has been said that Plato flies as well as walks, but this falls short of the truth; for he flies and walks at the same time, and is in the air and on firm ground in successive instants.