Describes a new theory of motivation and its applications to addiction and aversion. It assumes that many hedonic, affective, or emotional states are automatically opposed by CNS mechanisms which reduce the intensity of hedonic feelings, both pleasant and aversive. Opponent processes for most hedonic states are strengthened by use and weakened by disuse. These assumptions lead to deductions of many known facts about acquired motivation. The theory also suggests several new lines of research on motivation. It argues that the establishment of some types of acquired motivation does not depend on conditioning and is nonassociative in nature. Relationships between conditioning processes and postulated opponent processes are discussed. It is argued that the data on several types of acquired motivation, arising from either pleasurable or aversive stimulation, can be fruitfully reorganized and understood within the framework provided by the opponent-process model.(34 ref)(PsycINFO Database Record (c) 2016 APA, all rights reserved)