Karl Wilhelm Friedrich (after 1814: von) Schlegel (; German: [ˈfʁiːdʁɪç ˈʃleːgl̩]; 10 March 1772 – 12 January 1829) was a German poet, literary critic, philosopher, philologist, and Indologist. With his older brother, August Wilhelm Schlegel, he was one of the main figures of Jena Romanticism.
Born into a fervently Protestant family, Schlegel rejected Christianity as a young man in favor of atheism and individualism. He entered university to study law but instead focused on classical literature. He began a career as a writer and lecturer, and founded journals such as Athenaeum. In 1808 Schlegel converted to Catholicism. His religious conversion ultimately led to his estrangement from family and old friends. He moved to Austria in 1809, where he became a diplomat and journalist in service of Klemens von Metternich, the Foreign Minister of the Austrian Empire. Schlegel died in 1829, at the age of 56.
Schlegel was a promoter of the Romantic movement and inspired Samuel Taylor Coleridge, Adam Mickiewicz and Kazimierz Brodziński. The first to notice what became known as Grimm's law, Schlegel was a pioneer in Indo-European studies, comparative linguistics, and morphological typology, publishing in 1819 the first theory linking the Indo-Iranian and German languages under the Aryan group.
Karl Friedrich von Schlegel was born on 10 March 1772 at Hanover, where his father, Johann Adolf Schlegel, was the pastor at the Lutheran Market Church. For two years he studied law at Göttingen and Leipzig, and he met with Friedrich Schiller. In 1793 he devoted himself entirely to literary work. In 1796 he moved to Jena, where his brother August Wilhelm lived, and here he collaborated with Novalis, Ludwig Tieck, Fichte, and Caroline Schelling, who married August Wilhelm. Novalis and Schlegel had a famous conversation about German idealism. In 1797 he quarreled with Schiller, who did not like his polemic work.
Schlegel published Die Griechen und Römer (The Greeks and Romans), which was followed by Geschichte der Poesie der Griechen und Römer (History of the Poesy of the Greeks and Romans) (1798). Then he turned to Dante, Goethe, and Shakespeare. In Jena he and his brother founded the journal Athenaeum, contributing fragments, aphorisms, and essays in which the principles of the Romantic school are most definitely stated. They are now generally recognized as the deepest and most significant expressions of the subjective idealism of the early Romanticists. After a controversy, Friedrich decided to move to Berlin. There he lived with Friedrich Schleiermacher and met Henriette Herz, Rahel Varnhagen, and his future wife, Dorothea Veit, a daughter of Moses Mendelssohn and the mother of Johannes and Philipp Veit. In 1799 he published Lucinde, an eccentric and unfinished novel, which is remarkable as an attempt to transfer to practical ethics the Romantic demand for complete individual freedom. Lucinde, in which he extolled the union of sensual and spiritual love as an allegory of the divine cosmic Eros, caused a great scandal by its manifest autobiographical character, mirroring his liaison with Dorothea Veit, and it contributed to the failure of his academic career in Jena  where he completed his studies in 1801 and lectured as a Privatdozent on transcendental philosophy. In September 1800 he met four times with Goethe, who would later stage his tragedy Alarcos (1802) in Weimar, albeit with a notable lack of success.
In June 1802 he arrived in Paris, where he lived in the house formerly owned by Baron d'Holbach and joined a circle including Heinrich Christoph Kolbe. He lectured on philosophy in private courses for Sulpiz Boisserée, and under the tutelage of Antoine-Léonard de Chézy and linguist Alexander Hamilton he continued to study Sanskrit and the Persian language. He edited the journal Europa (1803), where he published essays about Gothic architecture and the Old Masters. In April 1804 he married Dorothea Veit in the Swedish embassy in Paris, after she had undergone the requisite conversion from Judaism to Protestantism. In 1806 he and his wife went to visit Aubergenville, where his brother lived with Madame de Staël.
In 1808, he published an epoch-making book, Über die Sprache und Weisheit der Indier (On the Language and Wisdom of India). Here he advanced his ideas about religion and importantly argued that . Schlegel compared Sanskrit with Latin, Greek, Persian and German, noting many similarities in vocabulary and grammar. The assertion of the common features of these languages is now generally accepted, albeit with significant revisions. There is less agreement about the geographic region where these precursors settled, although the Out-of-India model has generally become discredited.
In 1808, he and his wife joined the Roman Catholic Church in the Cologne Cathedral. From this time on, he became more and more opposed to the principles of political and religious liberalism. He went to Vienna and in 1809 was appointed imperial court secretary at the military headquarters, editing the army newspaper and issuing fiery proclamations against Napoleon. He accompanied archduke Charles, Duke of Teschen to war and was stationed in Pest during the War of the Fifth Coalition. Here he studied the Hungarian language. Meanwhile, he had published his collected Geschichte (Histories) (1809) and two series of lectures, Über die neuere Geschichte (On Recent History) (1811) and Geschichte der alten und neuen Literatur (On Old and New Literature) (1815). In 1814 he was knighted in the Supreme Order of Christ.
In collaboration with Josef von Pilat, editor of the Österreichischer Beobachter, and with the help of Adam Müller and Friedrich Schlegel, Metternich and Gentz projected a vision of Austria as the spiritual leader of a new Germany, drawing her strength and inspiration from a romanticised view of a medieval Catholic past.
Following the Congress of Vienna (1815), he was councilor of legation in the Austrian embassy at the Frankfurt Diet, but in 1818 he returned to Vienna. In 1819 he and Clemens Brentano made a trip to Rome, in the company of Metternich and Gentz. There he met with his wife and her sons. In 1820 he started a conservative Catholic magazine, Concordia (1820–1823), but was criticized by Metternich and by his brother August Wilhelm, then professor of Indology in Bonn and busy publishing the Bhagavad Gita. Schlegel began the issue of his Sämtliche Werke (Collected Works). He also delivered lectures, which were republished in his Philosophie des Lebens (Philosophy of Life) (1828) and in his Philosophie der Geschichte (Philosophy of History) (1829). He died on 12 January 1829 at Dresden, while preparing a series of lectures.
Friedrich Schlegel's wife, Dorothea von Schlegel, authored an unfinished romance, Florentin (1802), a Sammlung romantischer Dichtungen des Mittelalters (Collection of Romantic Poems of the Middle Ages) (2 vols., 1804), a version of Lother und Maller (1805), and a translation of Madame de Staël's Corinne (1807–1808) — all of which were issued under her husband's name. By her first marriage she had two sons, Johannes and Philipp Veit, who became eminent Catholic painters.
Friedrich Schlegel's Sämtliche Werke appeared in 10 vols. (1822–1825); a second edition (1846) in 55 vols. His Prosaische Jugendschriften (1794–1802) have been edited by J. Minor (1882, 2nd ed. 1906); there are also reprints of Lucinde, and F. Schleiermacher's Vertraute Briefe über Lucinde, 1800 (1907). See R. Haym, Die romantische Schule (1870); I. Rouge, F. Schlegel et la genie du romantisme allemand (1904); by the same, Erläuterungen zu F. Schlegels „Lucinde“ (1905); M. Joachimi, Die Weltanschauung der Romantik (1905); W. Glawe, Die Religion F. Schlegels (1906); E. Kircher, Philosophie der Romantik (1906); M. Frank "Unendliche Annäherung". Die Anfänge der philosophischen Frühromantik (1997); Andrew Bowie, (1997).From Romanticism to Critical Theory: The Philosophy of German Literary Theory