Guaraní (), specifically the primary variety known as Paraguayan Guarani ( "the people's language"), is a South American language that belongs to the Tupi–Guarani family of the Tupian languages. It is one of the official languages of Paraguay (along with Spanish), where it is spoken by the majority of the population, and where half of the rural population are monolingual speakers of the language. It is spoken by communities in neighboring countries, including parts of northeastern Argentina, southeastern Bolivia and southwestern Brazil, and is a second official language of the Argentine province of Corrientes since 2004; it is also an official language of Mercosur. Guaraní is one of the most widely spoken American languages, and remains commonly used among the Paraguayan people and neighboring communities. This is unique among American languages; language shift towards European colonial languages (in this case, the other official language of Spanish) has otherwise been a nearly universal phenomenon in the Western Hemisphere, but Paraguayans have maintained their traditional language while also adopting Spanish. Jesuit priest Antonio Ruiz de Montoya, who in 1639 published the first written grammar of Guarani in a book called Tesoro de la lengua guaraní (Treasure of the Guarani Language / The Guarani Language Thesaurus), described it as a language "so copious and elegant that it can compete with the most famous [of languages]". The name "Guarani" is generally used for the official language of Paraguay. However, this is part of a dialect chain, most of whose components are also often called Guarani. History While Guarani, in its Classical form, was the only language spoken in the expansive missionary territories, Paraguayan Guaraní has its roots outside of the Jesuit Reductions. Modern scholarship has shown that Guarani was always the primary language of colonial Paraguay, both inside and outside the reductions. Following the expulsion of the Jesuits in the 18th century, the residents of the reductions gradually migrated north and west towards Asunción, a demographic shift that brought about a decidedly one-sided shift away from the Jesuit dialect that the missionaries had curated in the southern and eastern territories of the colony. By and large, the Guaraní of the Jesuits shied away from direct phonological loans from Spanish. Instead, the missionaries relied on the agglutinative nature of the language to formulate calque terms from native morphemes. This process often led the Jesuits to employ complicated, highly synthetic terms to convey Western concepts. By