used for the wider family including Anatolian by those who consider that IE and Anatolian are comparable separate branches. Study methods The comparative method was formally developed in the 19th century and applied first to Indo-European languages. The existence of the Proto-Indo-Europeans had been inferred by comparative linguistics as early as 1640, while attempts at an Indo-European proto-language reconstruction date back as far as 1713. However, by the 19th century, still no consensus had been reached about the internal groups of the IE family. The method of internal reconstruction is used to compare patterns within one dialect, without comparison with other dialects and languages, to try to arrive at an understanding of regularities operating at an earlier stage in that dialect. It has also been used to infer information about earlier stages of PIE than can be reached by the comparative method. The IE languages are sometimes hypothesized to be part of super-families such as Nostratic or Eurasiatic. History Preliminary work The ancient Greeks were aware that their language had changed since the time of Homer (about 730BC). Aristotle (about 330BC) identified four types of linguistic change: insertion, deletion, transposition and substitution. In the 1st century BC, the Romans were aware of the similarities between Greek and Latin. In the post-classical West, with the influence of Christianity, language studies were undermined by the naïve attempt to derive all languages from Hebrew since the time of Saint Augustine. Prior studies classified the European languages as Japhetic. One of the first scholars to challenge the idea of a Hebrew root to the languages of Europe was Joseph Scaliger (1540–1609). He identified Greek, Germanic, Romance and Slavic language groups by comparing the word for "God" in various European languages. In 1710, Leibniz applied ideas of gradualism and uniformitarianism to linguistics in a short essay. Like Scaliger, he rejected a Hebrew root, but also rejected the idea of unrelated language groups and considered them all to have a common source. Around the 12th century, similarities between European languages became recognised. In Iceland, scholars noted the resemblances between Icelandic and English. Gerald of Wales claimed that Welsh, Cornish, and Breton were descendants of a common source. A study of the Insular Celtic languages was carried out by George Buchanan in the 16th century and the first field study was by Edward Llwyd around 1700. He published his work in 1707, shortly after translating a study