cognitive dissonance mental discomfort arising from conflicting beliefs or attitudes held simultaneously. Leon Festinger, who originated the theory of cognitive dissonance in a book of that title (1957), suggested that cognitive dissonance has motivational characteristics. Suppose a person is contemplating moving to a new city. She is considering both Birmingham and Boston. She cannot move to both, so she must choose. Dissonance is experienced by the person if in choosing, say, Birmingham, she acquires knowledge of bad or unwelcome features of Birmingham and of good or welcome aspects of Boston. The amount of dissonance depends on the relative intensities of dissonant elements. Hence, if the only dissonant factor is her learning that Boston is cooler than Birmingham, and she does not regard climate as important, she will experience little dissonance. Dissonance may occur in several sorts of psychological states or processes, although the bulk of research in cognitive dissonance theory has been on dissonance in choice and on the justification and psychological aftereffects of choice. Cognitive dissonance may be involved in two phenomena of interest to philosophers, namely, self-deception and weakness of will. Why do self-deceivers try to get themselves to believe something that, in some sense, they know to be false? One may resort to self-deception when knowledge causes dissonance. Why do the weak-willed perform actions they know to be wrong? One may become weak-willed when dissonance arises from the expected consequences of doing the right thing. G.A.G.