A rule is a context dependent relationship between state values and some prediction. Rules typically take the form of an {IF:THEN} expression, (e.g. {"IF 'condition' THEN 'action'}," or as a more specific example, "{IF 'red' AND 'octagon' THEN 'stop-sign'}"). A critical concept in LCS and rule-based machine learning alike, is that an individual rule is not in itself a model, since the rule is only applicable when its condition is satisfied. Think of a rule as a "local-model" of the solution space.