At http://blog.ruleml.org/post/32629706-the-sad-state-concernin... Kowalski summarizes his theory of the classification of rules (within production logic systems) in to a triple typology, and suggests that the last of these types, which he terms reactive rules, are more fundamental, and "the driving force of life". These are rules which define a subsequent action or state from current conditions, ie. "if hungry then eat".

To fully grasp the idea it is important to understand the different natures of logic programming versus imperative/procedural programming... there is not really an if-then-else-style (ie. control flow oriented) program state. Rather, the programmer tends to throw a bunch of formal rules at a 'solver' which simply determines the result.