This paper proposes a formal semantic approach to Slavic verbal prefixes. Slavic verbal prefixes form a highly heterogeneous class. They fulfill a wide range of functions; they can contribute quantificational, temporal, aspectual or temporal interpretations. Given the heterogeneous nature of the prefixes, a natural question to ask is whether it is possible to make any generalizations regarding their semantics. In this paper, I put forward The Scale Hypothesis, 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-. Further, a range of parameters is discussed along which prefixes are predicted to vary under The Scale Hypothesis.