The dynamic view on the semantics of natural language, though stemming already from the seventies, has developed into a widely studied subject in the second half of the eighties. At present, the unification of various dynamic theories constitutes an important issue. In this paper, two theories are compared, viz. update semantics, and dynamic predicate logic. In section 1 a general characterization of the idea of a dynamic semantics for natural language is given which subsumes these two theories. Sections 2 and 3 are devoted to short expositions of each of them. In the final section 4 a comparison is made.