He survived into the era of Kant, Goethe and Schiller, but he was not of it, and it would have been unreasonable to expect that he should in old age pass beyond the limits of his own epoch. As Germans now generally admit, it was better that he let their literature alone, since, left to itself, it became a thoroughly independent product. Indirectly he powerfully promoted it by deepening the national life from which it sprang. At a time when there was no real bond of cohesion between the different states, he stirred among them a common enthusiasm; and in making Prussia great he laid the foundation of a genuinely united empire. BIBLIOGRAPHICAL NOTE.--The main sources for the biography of Frederick the Great are his own works, which, in the words of Leopold von Ranke, "deal with the politics and wars of the period with the greatest possible objectivity, i.e. truthfulness, and form an imperishable monument of his life and opinions." A magnificent edition of Frederick's complete works was issued (1846-1857), at the instance of Frederick William IV., under the supervision of the historian Johann D. E. Preuss (1785-1868). It is in thirty volumes, of which six contain verse, seven are historical, two philosophical, and three military, twelve being made up of correspondence. So long as the various state archives remained largely inaccessible historians relied upon this as their chief authority. Among works belonging to this period may be mentioned Thomas Carlyle, _History of Frederick II. of Prussia_ (6 vols., London, 1858-1865); J. G. Droysen, _Friedrich der Grosse_ (2 vols., Leipzig, 1874-1876, forming part V. of his _Geschichte der preussischen Politik_); Ranke, _Friedrich II., Koenig von Preussen_ (_Werke_, vols. li. and lii.). A great stimulus to the study of Frederick's history has since been given by the publication of collections of documents preserved in various archives. Of these the most important is the great official edition of Frederick's political correspondence (Berlin, 1879), of which the thirty-first vol. appeared in 1906. Of later works, based on modern research, may be mentioned R. Koser, _Koenig Friedrich der Grosse_, Bd. 2 (Stuttgart, 1893 and 1903; 3rd ed., 1905); Bourdeau, _Le Grand Frederic_ (2 vols., Paris, 1900-1902); L. Paul-Dubois, _Frederic le Grand, d'apres sa correspondance politique_ (Paris, 1903); W. F. Reddaway, _Frederick the Great and the Rise of Prussia_ (London, 1904). Of the numerous special studies may be noticed E. Zeller, _Friedrich der Grosse als Philosoph_ (Berlin, 1886); H. Pigge, _Die Staatstheorie Friedrichs des Grossen_ (Muenster, 1904); T. von Bernhardi, _Friedrich der Grosse als Feldherr_ (2 vols., Berlin, 1881); Ernest Lavisse, _La Jeunesse du Grand Frederic_ (Paris, 1891, 3rd ed., 1899; Eng. transl., London, 1891); R. Brode, _Friedrich der Grosse und der Konflikt mit seinem Vater_ (Leipzig, 1904); W.