Though most of his conclusions on etymology and comparative linguistics were proven to be incorrect, his works remain valuable for vast observational data.

He did not complete the gymnasium education and withdrew in 1869 but continued to study the languages translating various texts from Latin, German, Polish.

[7] As a gifted student, Jaunius was sent to the Saint Petersburg Roman Catholic Theological Academy even prior the completion of the priest seminary, but he failed exams in Russian language, geography, and history.

[8] Several noted linguists and philologists, including Lucian Müller, Franz Anton Schiefner, Daniel Chwolson, and Nikolai Petrovich Nekrasov [ru], taught at the academy.

[9] By the time he graduated from the academy, he knew eight languages (Lithuanian, Russian, Polish, Latin, Ancient Greek, Sanskrit, German, French).

In 1879, the Saint Petersburg Academy of Sciences asked Jaunius to review a collection of Lithuanian folk songs compiled by Antanas Juška.

Jaunius returned to the priest seminary in October 1885 as teacher of moral theology, homiletics, and Lithuanian language.

[15] Jaunius devoted his time to linguistic studies and published several articles on the dialects of the Lithuanian language.

[19] Jaunius possibly targeted Kazan because it had a university where Alexander Alexandrov [ru], who had written on the Lithuanian language, was a professor.

When he could not hold a mournful mass for Tsar Alexander III of Russia due to his poor health, Tsarist authorities suspected political motives and wanted to exile him to Siberia.

[22] He petitioned the Governor of Kaunas for a monthly disability pay and was hoping to get a teaching job at the Saint Petersburg Roman Catholic Theological Academy.

He helped Eduards Volters with the publication of the postil of Mikalojus Daukša and delivered three lectures on Lithuanian word endings to the Neo-Philological Society in 1898.

[26] In 1903, the Jagiellonian University in Kraków offered him chairmanship of the newly formed Lithuanian language section but Jaunius refused possibly due his deteriorating health – he complained of poor eyesight, weak heart, pain in legs, auditory issues, etc.

[28] When Jonas Basanavičius asked him why he made so many notes in book margins instead of writing them down in a notebook, Jaunius replied that he was afraid of white paper and almost never used blank sheets.

Afraid that his knowledge was wasting, professors Filipp Fortunatov and Aleksey Shakhmatov organized funding for a private secretary.

[18] His reply that the Lithuanian language used a Latin–Lithuanian alphabet (and not Latin–Polish) was added the case file during government debates that led to the lifting of the ban in early 1904.

[35] Jan Niecisław Baudouin de Courtenay and Alexander Alexandrov [ru] wrote articles about Jaunius' life that were published as separate booklets.

[36] Lithuanian activists started a fundraising campaign to erect a monument (built in 1913 by sculptor Antanas Aleksandravičius) and to publish his works.

[31] Jan Niecisław Baudouin de Courtenay praised Jaunius' deep knowledge of multiple languages and his ability to take in this vast information, systematize it, and arrive to broad conclusions.

[43] While the grammar was written as a practical textbook for Lithuanian clerics, it contained new and deep insights into the living language and was praised by Jonas Jablonskis for its wealth of knowledge.

[44] Jablonskis used Jaunius' grammar extensively when preparing his own publication that became the key work in creating the standard Lithuanian language.

He was not very successful in this area as he often used awkward compound words or simply translated Latin terms without fully adapting them to the Lithuanian language.

All of these articles were written in Russian and published in an annual publication Memorial Book of the Kovno Governorate (Памятная книжка Ковенской губернии), the yearbook of the Kaunas government.

[54] Būga wrote down 3,043 pages in six volumes of Jaunius' teachings on Lithuanian, Latvian, and Prussian languages and their Baltic proto-language.

[56] For example, when explaining etymology of a certain word, Jaunius often searched for equivalents in the trendy Greek or Armenian languages instead of closer neighbors.