The study of sound patterns goes back thousands of years. Pāɳini and his Indic contemporaries formulated phonetic laws and phonological rules over 2,000 years ago. Under the influence of Hindu and Chinese grammarians, King Seijong (1417–50) and his court advisors devised a writing system for Korean, hankul, which demonstrates a clear understanding of the phonemic principle and a sophisticated use of distinctive phonological features. Building on Chén Dì's (1541–1617) principle of historical change, early Qing dynasty scholars like Gù Yánw (1613–82) and Duàn Yùcái (1735–1815) made significant steps in the reconstruction of Old Chinese sound patterns. On the other side of the world, Sir William Jones (1746–94) observed in 1786 that Sanskrit, Greek, and Latin showed similarities of form suggestive of a family relationship. This observation inspired the European scholars Franz Bopp (1791–1867) and Jacob Grimm (1785–1863), forefathers of the neogrammarian movement.