The Inscape Environment research project addresses issues in supporting the development of large systems by large numbers of programmers. One aspect of this research is the “constructive use” of formal module interface specifications - that is, given that you have formal specifications, what can you do with them. In Inscape, the specifications form the basis for providing an environment that is knowledgeable about the process of developing and evolving software systems, an environment that works in symbiosis with the programmer to develop and evolve a software system.In this discussion, I present how Inscape uses operation specifications (based on Hoare's input/output predicate approach) as the basis for synthesizing the interfaces for such complex languages statements as sequence, selection and iteration. In each of these statements, the synthesized interface is a function of the component interfaces.I first present the basic rules for interface specification use and the logical framework for interface propagation and error detection. I then define the rules for propagating the interfaces for sequence, selection, iteration and operation. Finally, I define notions of “implementation completeness and correctness”.