The theory of problem-solution patterning is already well established for a wide range of genres and at macrostructure and microstructure levels of communication. That theory has, however, largely failed to account for interactive solution-problems: where a solution is or causes a problem to another person, group or thing. This paper establishes the major parameters of this sub-theory of problem-solution structures and the related grammar and signalling. For informal writing in the natural sciences, solution-problems are shown to apply to environmental concerns, predator-prey relations and cause-effect relations. More generally the principles are extended to cover third-party involvement, friends and enemies and iatrogenic solution-problems. The sub-theory of structures and linguistic signalling outlined here applies to many genres – not just those in the natural sciences, but also in news and business reports, and general journalism. Studies of the structures and signalling of politics and fictional works (cartoons, sitcoms, soap operas, movies, novels, etc.) would be natural extensions for the principles explained.