The property of a (formal) development method which gives the development process the potential for productivity is compositionality, compositional development methods for concurrent system are elusive because of inference. A companion paper shows how object-based concepts can be used to provide a designer with control over inference and proposes a transformational style of development in which concurrency is introduced only in the final stages of design. That approach relies on restrictions to the object graphs which can arise and works for systems which involve limited inference. The current paper discusses the problems of inference and shows how a suitable logic can be used to reason-during design-about those systems where interference plays an essential role. Here again, concepts are used in the design notation which are taken from object-oriented languages since they offer control of granularity and ways of pinpointing inference. A further paper is in preparation which discusses the semantics of the object-based design notation