The article is concerned with semantic functions of the postverb up – the second component of English verbs of the type move up, fix up, round up (Vup-s) from the point of view of changing the lexical meaning of the verb and its aspectual characteristics in terms of terminativeness / durativeness, and modes of action. Analysis and classification of Vup-s according to their lexical meaning and modes of action reveal the systemic character of the language. Vup-s are viewed as derivational units – analytic words – in the plane of word formation theory.