Analysis of information sources in references of the Wikipedia article "Imperfective aspect" in English language version.
The Slavic perfective prefixes originally signaled locative notions which made the verb telic (just as go out, go through, and eat up are telic in English).
The imperfective suffix in Slavic languages corresponds to the English progressive (cf. Borer 2005). [...] According to Arsenijevic the meaning of the Slavic imperfective suffix is slightly more general than that of the progressive.