A statement specifying what is permissible under given circumstances. E.g., the rules of chess spell out how a piece can move, the rules of grammar state which linguistic
transformations (e.g., from active into passive sentence construction) are possible (
see rewrite rules ). Unlike
laws -which are inevitably deterministic- rules tend to leave a user, whether he be a chess player or a native speaker, alternatives and specify
constraints within which he may chose. Rules do not imply obligation to act. The search for rules rather than laws distinguishes two schools in
communication research, the
cybernetics of observing
systems from the cybernetics of observed systems, and perhaps the social sciences from the natural sciences. (
Krippendorff )
