The interest in past helped the development of comparative research and new ideas. Thus Rasmus Rask (1787-1832) wrote about phonological relationships between Greek and Old Norse words, for example pate : father (ibid). Hock explained (37-38) that although Rask discovered that the most fascinating feature of PIE aspirates bh, dh, gh is “their aspiration, rather than the presence or absence of feature [voice]”, related sound changes were later named the Grimm’s Law, because Jacob Grim “most successfully brought them [the changes] to the attention of the linguistic community”. In the second edition of his grammar (1822), which was strongly influenced by the work of Rask, Jacob Grimm “formulated the rules that set the pattern for scientific historical phonology” (Lehmann 28).
Grimm’s sound change description had flaws. The first one was the absence of the shift of p t k after Germanic fricatives, but in 1830s it was clear to most linguists that this change did not affect clusters of consonants after Germanic fricatives (ibid 30). After that, Hermann Grassman (1809-77) solved the problem of the aspirates: he defined the loss of aspiration in Greek and Latin. This was followed by Karl Verner’s (1846-96) explanation on how Indo-European voiceless stops in a voiced context, if not preceded by an accent, become voiced fricatives.
This investigation in phonetic change was one of the most fascinating periods in the early era of historical linguistics, and surely a most notable one. New discoveries continued after the well-known work of Franz Bopp (1791-1867) was published, about the Sanskrit system of conjugation compared with that of Greek.
The consequence of these developments was that the new linguistic discipline was changing from a descriptive to a more investigative and more systematic research.
The definitive establishment of the systematic character of historical linguistics was given to it by the Neogrammarians. Karl Brugmann (1849-1919) was one of the most prominent representatives of the Neogrammarian hypothesis, which was devised by a group of linguist in Leipzig and Munich. As language materials and knowledge about linguistics were becoming more abundant, the Neogrammarians believed they had “enough evidence to declare that sound change was invariably regular – that is, that a given sound in a given context in a given language always changed in the same way, without exception” (Trask 111).
The following stage in the development of historical linguistics was the focus on the social and psychological aspects of the language change. In one of his essays Brugmann defines language as having double nature: psychological and physical. Brugmann criticised his predecessors for not paying attention to the psychological side of speech, which was, according to this scholar, important for fuller understanding of the sound change (Lehmann 31). Indeed, this standpoint will later initiate psycholinguistic examination of language. Brugmann was very critical of the works of that time, stating that linguists needed to study living languages as well, not only “dead” ones. He formulated “two most important principles of the neogrammarian movement: first, every sound change takes place according to laws that admin no exception. Second, form association, that is, the creation of new forms by analogy, plays a very important role in the life of language” (Lehmann 31).
One of the best-known linguists of all times is Ferdinand de Saussure (1857-1913). His lectures Cours de linguistiqe generale (1916), published by his students, explained how Saussure referred “to language in general as langage, to the underlying structure as langue and to spoken language as parole” (Lehmann 34). The theoretical frame Saussure constructed enabled linguists in general to distance themselves from “psychological emphasis of the neogrammarians”.
At the beginning of 19th century sociology as a discipline began its development, and affected other humanities. Linguistics was not an exception. Antonie Meillet, Saussure’s student, in his famous Oslo lectures (1924) claimed that “a language cannot be understood if we do not have an idea of the conditions under which the people who use it live” and further, that linguists are interested “not in the norms but in the way in which language is used”, as cited by Lehmann (35). This greatly contributed to dialectology, and to the research on how a language changes in contact with speakers of a different language or dialect.