In 1996 he co-authored with Walter Mischel a paper presenting the "cognitive-affective system theory of personality", stating that if people's behaviors reflect their personalities, and if their personalities remain relatively unchanged across situations, then it should be possible to predict what a person is like in one situation from knowing what she or he is like in another, based on stable and distinctive, individual patterns, called behavioral signatures.
^ abMischel, W. & Shoda, Y. (1995). A cognitive-affective system theory of personality: Reconceptualizing situations, dispositions, dynamics, and invariance in personality structure. Psychological Review, 102, 246-268.