This paper proposes a formal semantic approach to Slavic verbal prefixes. A hypothesis is put forward according to which a verbal prefix imposes a relation between two degrees on a scale. One is a degree associated with the event denoted by the verbal predicate. The other one is the standard of comparison, contributed by a linguistic expression that appears in the sentence, or by the context. The scale to which the prefix applies is most typically contributed by the linguistic environment in which the prefix appears. The paper demonstrates how the proposed analysis applies to two specific morphemes in Russian: the prefixes pod- and do-.
