The lack of declensional endings is the most characteristic trait of the modern Bulgarian language and its dialects. It seems exotic on the background of the remaining Slavic languages but in the large Indo-European language family the development from synthetism to analytism is a rule of which only Slavic and Baltic languages make an exception. Some scholars define the transition from synthetism to analytism as a process of dispatching the nominal flexion, during which part of the grammatical information (syntactic) is transferred to link-words (most commonly prepositions and particles). This is why all analytic languages develop a common form after prepositions (casus generalis), partly or completely fixed word order, pronoun particles for the marking of objects. The main precondition for the common Indo-European development towards the existence of an extended prepositional-declensional use is to be found in the Indo-European protolanguage. The author proposed not only a survey of the well known hypotheses but some new arguments for the appearance and development of Bulgarian analyitsm.