The Modern Bulgarian Language

Even though the Bulgarian language is closely related to all other Slavic languages, through the course of the centuries it has developed many specific traits and characteristics that clearly distinguish it among the other members of the Slavic family. First and foremost, Bulgarian has dispensed with the case system of the nouns, whereas all other Slavic languages have preserved their case systems.
Prepositions have replaced cases as a way of showing the grammatical relationships between different parts of a sentence. Second, Bulgarian has developed a system of definite articles (such as the English the) that come after the noun - for example kniga (book) and knigata (the book), while no other Slavic language has developed such a system. Third, Bulgarian has lost the infinitive form of all verbs, whereas the other Slavic languages have kept it. Fourth, Bulgarian has preserved a wide array of verb tenses, while all other Slavic languages have significantly simplified their verb-tense systems.