This paper focuses on Tarski`s declarative semantics and their usefulness in the design of a modeling language. We introduce the principles behind Tarski`s approach to semantics and explain what advantages this offers in the context of modeling languages. Using sentential logic we demonstrate the necessity and sufficiency of Tarski`s semantics for effectively addressing several issues that arise in the design of modeling languages. We explain what role Tarski`s semantics play in the organization of a modeling language. This role is compared to the analogous roles of denotational semantics and operational semantics. We show that in the context of a modeling language Tarski`s semantics are complementary to the other two kinds of semantics. The paper is intended to assist modeling language researchers and designers, particularly in connection with the UML - a language that in its current form does not feature Tarski`s declarative semantics.