rural large-landowning class, known as the szlachta, was largely Polish-speaking. Documents soon took on many Polish characteristics superimposed on Ruthenian phonetics. Polish rule and education also involved significant exposure to the Latin language. Much of the influence of Poland on the development of the Ukrainian language has been attributed to this period and is reflected in multiple words and constructions used in everyday Ukrainian speech that were taken from Polish or Latin. Examples of Polish words adopted from this period include zavzhdy (always; taken from old Polish word zawżdy) and obitsiaty (to promise; taken from Polish obiecać) and from Latin (via Polish) raptom (suddenly) and meta (aim or goal). Significant contact with Tatars and Turks resulted in many Turkic words, particularly those involving military matters and steppe industry, being adopted into the Ukrainian language. Examples include torba (bag) and tyutyun (tobacco). Due to heavy borrowings from Polish, German, Czech and Latin, early modern vernacular Ukrainian (prosta mova, "simple speech") had more lexical similarity with West Slavic languages than with Russian or Church Slavonic. By the mid-17th century, the linguistic divergence between the Ukrainian and Russian languages had become so significant that there was a need for translators during negotiations for the Treaty of Pereyaslav, between Bohdan Khmelnytsky, head of the Zaporozhian Host, and the Russian state. By the 18th century, Ruthenian had diverged into regional variants, developing into the modern Belarusian, Rusyn, and Ukrainian languages. Chronology The accepted chronology of Ukrainian divides the language into Old, Middle, and Modern Ukrainian. George Shevelov explains that much of this is based on the character of contemporary written sources, ultimately reflecting socio-historical developments, and he further subdivides the MU period with Early and Late phases. Proto-Ukrainian (abbreviated PU, Ukrainian: , until the mid-11th century), with no extant written sources by speakers in Ukraine. Corresponding to aspects of Old East Slavic. Old Ukrainian (OU, or , mid-11th to 14th c., conventional end date 1387), elements of phonology are deduced from written texts mainly in Church Slavic. Part of broader Old East Slavic. Middle Ukrainian ( or , 15th to 18th c.), historically called Ruthenian. Early Middle Ukrainian (EMU, , 15th to mid-16th c., 1387–1575), analysis focuses on distinguishing Ukrainian and Belarusian texts. Middle Ukrainian (MU, , mid-16th to early 18th c., 1575–1720), represented by several vernacular language varieties as well as a version of Church Slavic. Late Middle Ukrainian (LMU, , rest of the