Abstract
This article is concerned with grammaticalization of prepositional elements in Slavic. It is argued that external prefixes are internal prefixes that underwent some grammaticalization process.
After discussing the grammaticalization of the Slavic prefix po- it is shown that the Czech future po- differs from Russian and Polish non-future prefixes. Furthermore, it is proposed that the presence of future po- in grammatical systems of Czech, Slovak, Slovenian and Sorbian is a result of diachronic grammaticalization processes induced primarily by the German-Slavic language contact in the Holy Roman Empire.