1. An ignition timing control method responsive to a sensed knock condition in internal combustion engine cylinders, comprising the steps of: determining a spark retard command in response to the sensed knock condition; sensing a predetermined set of engine operating conditions; setting a plurality of membership functions based on the sensed predetermined set of engine operating conditions; applying the set plurality of membership functions to a fuzzy inference engine having a knowledge rulebase for generating a set of truths responsive to the application of the set plurality of membership functions; normalizing the set of truths according to the relative degree each of the set of truths indicates an engine knock condition; positioning the normalized set of truths according to the absolute degree each of the set of truths indicates an engine knock condition; calculating a spark retard adjustment as a predetermined function of the normalized, positioned set of truths; adjusting the spark retard command in accord with the calculated spark retard adjustment; adapting a learned spark retard value, by (a) selecting an active learning cell, (b) adjusting a learned spark retard value corresponding to the active learning cell as a predetermined function of both the sensed knock condition and the set of truths; modifying the spark retard command in accord with the adjusted learned spark retard value; and controlling ignition timing in accord with the spark retard command.